C55, /3/A! NESS 3ff NOAA TM NESS 35 A UNITED STATES DEPARTMENT OF COMMERCE PUBLICATION 6 ^SV .V NOAA Technical Memorandum NESS 35 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Environmental Satellite Service WASHINGTON, D.C. April 1972 Modified Version of the Improved TIROS Operational Satellite (ITOS D-G) A. SCHWALB NOAA TECHNICAL MEMORANDA National Environmental Satellite Service Series The National Environmental Satellite Service (NESS) is responsible for the estab- lishment and operation of the National Operational Meteorological Satellite System and of the environmental satellite systems of NOAA. The three principal Offices of NESS are Operations, Systems Engineering, and Research. NOAA Technical Memoranda NESS series facilitate rapid distribution of material that may be preliminary in nature and which may be published formally elsewhere at a later date. Publications 1 to 25 are in the former series, ESSA Technical Memoranda, National Environmental Satellite Center Technical Memoranda (NESCTM) . Beginning with 26, publications are now part of the series, NOAA Technical Memoranda, National Environ- mental Satellite Service (NESS) . Publications listed below are available from the National Technical Information Service, U.S. Department of Commerce, Sills Bldg., 5285 Port Royal Road, Springfield, Va. 22151. Price: $3.00 paper copy; $0.95 microfiche. Order by accession number shown in parentheses at end of each entry. ESSA Technical Memoranda NESCTM 6 Computer Processing of TOS Attitude Data. J. F. Gross, November 1968. (PB-182 125) NESCTM 7 The Improved TIROS Operational Satellite. Edward G. Albert, August 1968. (PB-180 766) Supplement No. 1. Characteristics of Direct Scanning Radiometer Data. Edward G. Albert, April 1969. (PB-183 965) NESCTM 8 Operational Utilization of Upper Tropospheric Wind Estimates Based on Meteorological Satellite Photographs. Gilbert Jager, Walton A. Follansbee, and Vincent J. Oliver, October 1968. (PB-180 293) NESCTM 9 Meso-Scale Archive and Products of Digitized Video Data From ESSA Satellites. Arthur L. Booth and V. Ray Taylor, October 1968. (PB-180 294) NESCTM 10 Annotated Bibliography of Reports, Studies, and Investigations Relating to Satellite Hydrology. D. R. Baker, A. F. Flanders, and M. Fleming, June 1970. (PB-194 072) NESCTM 11 Publications by Staff Members, National Environmental Satellite Center and Final Reports on Contracts and Grants Sponsored by the National Environmental Satellite Center 1968. January 1969. (PB-182 853) NESCTM 12 Experimental Large-Scale Snow and Ice Mapping With Composite Minimum Brightness Charts. E. Paul McClain and Donald R. Baker, September 1969. (PB-186 362) NESCTM 13 Deriving Upper Tropospheric Winds by Computer From Single Image, Digital Satellite Data. Charles S. Novak, June 1969. (PB-185 086) NESCTM 14 Study of the Use of Aerial and Satellite Photograrametry for Surveys in Hydrology. Everett H. Ramey, March 1970. (PB-191 735) NESCTM 15 Some Aspects of the Vorticity Structure Associated With Extratropical Cloud Systems. Harold J. Brodrick, Jr., May 1969. (PB-184 178) NESCTM 16 The Improvement of Clear Column Radiance Determination With a Supplementary 3.8p Window Channel. William L. Smith, July 1969. (PB-185 065) NESCTM 17 Vidicon Data Limitations. Arthur Schwalb and James Gross, June 1969. (PB-185 966) NESCTM 18 On the Statistical Relation Between Geopotential Height and Temperature- Pressure Profiles. W. L. Smith and S. Fritz, November 1969. (PB-189 276) NESCTM 19 Applications of Environmental Satellite Data to Oceanography and Hydrology. E. Paul McClain, January 1970. (PB-190 652) (Continued inside back cover) U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Environmental Satellite Service NOAA Technical Memorandum NESS 35 MODIFIED VERSION OF THE IMPROVED TIROS OPERATIONAL SATELLITE (ITOS D-G) A. Schwalb rfg "™°s^ ^nt of $n tr -r^.-000ir> cn *r co to lo •— coco O O o tr z O < (- o to to < tO > u- tO CD «- CN CO T LO LO (snoAi aonindwv ivnois (snoAi aonindwv ivnois H +> ro +J +> f0 w +J 5 -- 1 U ro ro O u U w O C tn -H CO -P CU -P D O u CD -P CD g O •H T3 fO I O CO C a; CQ CD •H Em O « £ - - CO T3 a cd ro >i i-i fO CD CO U -H O t3 4-1 CD £ X5 CD CD +J H 13 CD +J 0) •H CD fO M CD CO ro H ro iH C H &i -H ■H £ CO CO CD TJ CO 3 CD O £ «H 13 field of view of the instrument and changes the output level. This signal level restoration technique, using cold space as a reference, effectively removes the effect of self-emission of the optics. Radiometer Performance The IR channel data of the SR may be used to determine the equivalent black body temperature of the radiating surface. The ability to determine this temperature accurately is character- ized by the instrument noise equivalent differential temperature (NEAT). For practical purposes, NEAT may be considered as the temperature differential that can be discerned by the instrument when scanning from one uniform black body to another. In actu- ality, it is the blackbody energy differential of the target which, when sensed by the instrument, is equal to the root mean square (rms) noise level. When measuring warm targets, the NEAT's will be significantly lower (better) than when measuring cold targets since the instrument response is linear with input energy and system noise is not affected by target temperature. System noise, and therefore NEAT, is affected by the temperature of the radiometer itself so that no single number can be used to fully define the system NEAT. For this reason, published NEAT's are usually general and represent conditions at a nominal or worst case instrument operating temperature. When the bolom- eter temperature is 25°C (77.0°F) and the scene temperature is 300°K (80.6°F) (27°C), the NEaT is approximately 0.3°C (0.5°F); with the scene at 185°K, (-126. 4°F) (-88°C), the NEAT degrades to approximately 1.4°C (2.5°F) (both values determined at the instrument output) . Unfortunately, the spacecraft data link (tape recorders in particular) and ground handling of data fur- ther reduce the NEAT. A realistic estimate of NEAT for the 300° K target with bolometer at 25° C is 2 to 3 C° (3.6 to 5.4 F° ) , for the 185°K target, 8 to 10 (f (14.4 to 18.0 F° ) . The link analysis for a VHF receiving station is shown in table 7. Statistical processing of temperature data from a relatively uniform radiating surface (such as the sea surface) can reduce these uncertainties somewhat. 14 Automatic Picture Transmission (APT) Service For recording on the spacecraft recorder and for transmission to the local APT stations, the two channels of data, together with appropriate synchronization and telemetry from a single instrument, are combined into a single data stream. One channel of data will be transmitted during the time the scanner mirror rotates through 180 degrees (0.625 seconds). The alternate channel is transmitted during the remaining 0.625 seconds of the 360 degree mirror rotation. In practice this will be accomplish- ed by transmitting the infrared window data directly from the radiometer; the visible channel data from the same scanner will be tape recorded and played back one-half spin period (0.625 seconds) later. Table 4 contains the data timing information for the Scanning Radiometer APT transmission. This same infor- mation is shown schematically in fig. 7. Transmission link characteristics are summarized in tables 6, 7, 8, and 9. It should be noted that: 1. Seven pre-earth synchronization pulses (300-Hz rate) pre- cede each set of data (IR and visible) . 2. The post-earth synchronization porches (zero-level signals before and after the synchronization pulse) are 10 milliseconds in duration; the synchronization pulse itself is 30 milliseconds (this is one-half the duration of previous systems) . 3. The telemetry window (time period allotted for transmission of calibration data) for the IR channel (see E, figure 7) will consist entirely of voltage calibration steps (five steps, six levels, each of ten millisecond duration) ; the visible channel telemetry window (see E, figure 7) will consist of 25 lines, 11 of which will contain telemetry data for calibrating the IR out- put. The remaining 14 lines will be voltage calibration steps. The SR telemetry window assignments are shown in table 5. 15 c o •H CO Cfl •r-t 6 CO C (0 u ■u CO 3 O T> CO CO u •u o U CO 0) M M O U-l 00 c CO T3 O Q CO o H i-t i 0) 1— I 43 CO H Is i }H -P CD e CD .H CD -P Pi CO I LD X! (0 Eh c I o •l-l 3 4J o w Xl O a a 3 3 -u M r-l O a o Pi Z M c •fl i-l r-l a) c •£ a) S y 9 co c at Xl O O r-s (0 o c at oo a, i-i CO CO M a) u co 2 as a 00 CO C 00 5C i-l O o X) XI a> i— i a. e CO CO Xl 00 c 3 o EC u CO a CO a. cu 4) 00 <8 00 0) 00 IM •4-1 M cu 01 01 3 M M l-l 4-1 3 3 3 a) u 4-1 4-1 H CO CO CO oi M u M a 01 oi 0) R IX O. a oi 4-1 0) 01 0) x> c 3 X> O s 00 c 3 O XI 05 co 00 CO 3 o Xi Oi co ■a 3 O w X! & C CO o. CO CO 0) 01 o X c 01 r-l XI 0) • -d -a o 0) CJ 4-1 C co a> i—i X! H co cO 3 CO J> « C o 0) 01 rJ 4J CO CO >-. CO CO 01 3 01 i— I X! co 4J > CU 00 to e cu CJ r-l cd c CO 4-1 3 01 « CO CW r-l a o i-l c -a c co 3 4J CO -a XI C CO 01 CO >> -l co co c r-l r-l 6 3 . 4J X co CO >-, CO rC CJ cu -r-i x: X 4-1 3 a co O r-l O. 01 3 > CU XI r-4 C 01 co a. 4-1 01 CO XI X) 01 i-l 4-1 3 CO u *-x cu cu C 00 0) CO 00 4-1 r-l >> o r-l > 1—1 — > * CO 01 CJ i— I 4J •r-l cu eg C > O 01 i-l r-l r-l X o u a. r-l CO a. w X) CO X 3 4-1 > CO r-l CJ 3 ••-I o XI a co X •r-l 00 1-1 CU r-l U «J-I 3 4-1 C CO T-l r-l 01 4-1 & C e oj a) 4J 3 M r-l 4J CO co 3 C 4J -r-l o CO CU Xi 01 4-1 CO O 0) rC 4J 3 co u oo x C -H i-l r-l CO CO 3 CJ o x; o 01 X O CO CO l-l o oo eg M-i C X) c •r-l 1-1 3 cu CU CO CO i-l 0) i-l > X! X H 4J 01 r-H 00 iJ . c Xi ^ -H 3 -a- u CN -r-l 4-1 3 3 xi cr a c cu 4-1 CO U 3 CO CO CN Ij r-l 0) 01 CO CO 4J CU 3 oi C i-l 0) O r-l CO •r-l W O xl X CO CO -U l-l cu r-l O r-l (X 4J cu 3 C O XI C CJ cu CO O XI X -^ CJ l-l > o u Cu 05 Xi cu c c CO X o 0) • X -~x 4-1 r-l 01 CM C o c fl) 4J X 3 O &, 4-1 CU 3 r-l X •r-l 01 CO x; -h H > 01 r-l • 3 O 4J d CO M 3 Q) O a. xi C 01 -r-l 4-1 3 00 r^ C M i-l 4J CO cu 3 O 01 XI r-l OI H 4J c X) -H 01 4J XI U 01 01 4J > 4J c -^ o CO c 01 a) X r-l 4J c CO CO 0) 00 CO 3 o o Jj 0) X H c CO > 01 00 c •l-l r-l 0) 01 c 1-1 00 c cu 17 o • z oo oz c7)LU wS g_j o o ^fc — «• . .»- - is - J fc - fe e _ o o fet rO ?■* to -i— zuj^vj < - u. . oo INSTRUMENT RESTORE PERIOD -IR CHANNEL (COLD) | *» - BACK SCAN AND DATA OVERLAP (INDETERMINATE LEVEU FRONT PORCH 100% AMPI ITIinF f — — *T J -o rnUll 1 "UnV/n t\J\J fo MmrL_l 1 UUC 1 PLAYBACK SYNCHRONIZATION PULSE 4% AMP £ -T- § UJ— . 1 1 U , o 0] u BACK PORCH 100% AMPLITUDE 1 TELEMETRY WINDOW VOLTAGE CALIBRATION STEPS SHOWN -u. L ^-8 •H POST EARTH SPACE VIEW SUNSHIELD SHOULD APPEAR "Q \_= +J QUITE DARK BUT NOT BLACK V W •H -o S-l o — o QJ 1 -P U 10 -J \ 1 ^ zz << Id 0(0 IUX -u / o — o 01 a h -II- 1- o cDcr f — o c tz UJ / CD CO O tn s o — O tn _J z s _ ii ■H CO Eh < 1 ^ CO G QJ PRE EARTH SPACE VIEW (4% AMPLITUDE) 7 SYNCRONIZATION PULSES , VISIBLE CHANNEL ID •< "1- INSTRUMENT RESTORE , VISIBLE CHANNEL (LOW AMPLITUDE) "3 1 "a BACK SCAN AND DATA OVERLAP (INTERMEDIATE LEVEL) -S-l — o CD FRONT PORCH 100% LEVEL l~~ — UJ 2 CE PLAYBACK SYNCRONIZATION PULSE 4% AMPLITUDE 13 I" U o BACK PORCH 100% LEVEL 1 U. o — r s 2 uj H m C\J CO 1 UJ L 1 TELEMETRY WINDOW- VOLTAGE CALIBRATION STEPS POST EARTH SPACE VIEW (GRADUALLY APPEARS WARMER AS - co SCAN INCLUDES THE SUN SHIELD) Q - 1 1 • \ o — o ^y _*r \ - 0) _ 5-1 _ 3 — § cn _ •H UJ <^1 fa 2" > z<" S < * 5j . o fe O ) — o J C\J — UJ I -8 SPACE VIEW (COLD) [96% AMPLITUDE] m - 7 SYNCRONIZATION PULSES -i-zui^- < J* o % DEVIATION o o 18 Table 6. — Characteristics of VHF APT transmission Element Description Frequency Transmitter power output Antenna polarization Carrier modulation 137.50 or 137.62 MHz +0.005% — 2 possible transmission frequencies are assiqned to eliminate possible interference when 2 spacecraft are near the same areas at the same time. Only 1 frequency will be used at one time. Notification of the assigned frequency will be given in the "APT Predict" message 5 watts minimum Linear FM Peak carrier deviation RF spectrum bandwidth Subcarrier center frequency Subcarrier modulation Peak subcarrier modulation Baseband video bandwidth (design) 9 +1 KHz 2 7.2 KHz 2400 +0.014 Hz AM 90% IR data 450 Hz Visible data 900 Hz 19 ft ^-^ co QJ >1 CO u 0) ■H rO e O g •H G g P 3 1 CO co -H § (U cd u m +- c ro ft 0) 6 o H H K •H o a > m \ u CO ft CD 1 a e 0) ft r* p g 03 g •H >i H CO •H P CD f-H ro 6 rH p •H ro co -P u 1 CD iH iH > ro ro o cd u 13 CD ,— 1 H -P 4J PM re fO < e ■H ro ft P +J ffl CO ro > 1 1 W 13 CD .H X fO CC3 ro +J ro Q > CU CD l-l rH w X! •H CO o ■H CN > *— ' rH ro G •H ++ 6 ro +J a ro 13 ft H C > 01 H W ++ ro Ul P ro U ft H +J G CD 6 cd H W Cr G -H +J 3 X! ■H 5-1 P G u PQ "0 PQ PQ PQ PQ CQ m TJ T3 13 ■a CN O CN CN CN CN 10 LT> »£) r-> «tf r> r- ^ «tf on 13 CD i U ro CD rH P CD P 13 •rH « — e 5-1 w O U G co CD ro u to 13 5-1 CD 5-1 P w u G o O Eh CD u CD ft* CO a, U ft « ft ft ffi CO co CO > PQ 13 in n G •rH ft ft PQ 13 o p CO CD 5-1 CD > •H CD U CD 5-1 13 G 3 O 5-1 O PQ 13 P co CD 13 O 6 CD P PQ PQ 13 13 r» h PQ PQ 13 13 CN CN PQ PQ 13 13 rH m ro ro PQ PQ 13 13 LD Lfl ro ro .^ CO CO H H > > + o \ ft ft CO H H E " CD CD CD P 13 13 CO O O Nee CO H ft D H ro rH g ^ ro 5^ u 5-i o ro CD 2; PQ > O a a o o CN 00 a a o o ro C\ 0> rH E-t <1 P C « « CDO o rH in o ro oo o ro > -H 3 cr w ® © p 13 CD U G CD 5-1 CD IH CD 5-1 IH -H PQ 13 O • X CN P + 13 •H >i ^ X! 13 G CO ro U X CD X 13 e G p ro G X CD a CO \ ro CO X CD N CO HI ro CD o 5-1 o U 01 G e<73 CD G ro u u •rH ro G CD >i CO u •H O a> 13 •H > I H X ro ro c CD tp ft ■H CO o p I a ro \ CD CO ft * +- x: p 13 •H CD T3 13 G 3 ro P X ■H rH IQ a c e ro ro x CD CD CO co ro H X D ft N tu G O N in co ^ 20 ro > QJ v£> ro C •H g o o CN g g m m OP PQ CQ pq pq pq 13 13 13 13 13 -a 13 13 o co O O ^ IT) o CM 00 rH rH ro ^ CN rH o ro 1 | 1 <* rH 1 o + ■H + rH g pq 13 ro * pq 13 en rH + pq 13 o CN rH + pq 13 r> + c -H QJ g •H -P I rH r0 0J 5H Eh CM fa > I I 00 QJ U~) £ g pq pq pq pq pq pq pq pq 13 13 13 13 13 13 U 13 o 00 LO o ^ IT) o CN r- rH ro ro r> CN i-h r> ro I 1 ! ^t r-i I O + t-{ + rH 1 c •H ro ro G C q; -p c ro u OJ -p +J •H g CO c ro U Eh CO w o o •H -p (0 N ■H rH fO rH O CM CO CO o -p (0 a. c •H ro tn ro G C OJ P C fO U Q) > -H 0J O CO 01 CO CO o -p •H D u rH •H u D CN N O II il -P D 13 •P -H 13 a ro g 12 CD -P O PL. QJ CO •H O ;fi CD > ■H O; CO •H O c J-l o p u 0) u 17 -P P QJ QJ U QJ > > QJ 13 -H •H MH QJ 0J QJ CW U u O W Cm QJ QJ Pi & g pq 13 ro CTi -P Du C •H OJ CQ -rH O c +J c QJ r-\ fO > ■H D CJ 1 W pq 13 rH • ro g r4 QJ •H Jh ro O fa 21 X c •H QJ e •h i rH fO QJ U CM > Eh < 01 5h QJ +J 0) e u fO Ch c rd X QJ 03 rd X! TJ C fd 0) •H rH rd u X P w I I cr> QJ H X! iC (13 G •H 6 O QJ 0) rd U 4-> 03 rH o CO n QJ ■P QJ e rd rH rd PQ t3 X> en + CQ r-» CN + m o o CQ O o rH + CQ 13 vD r- CN + CQ •a r-> rH + •H 4-> nj u QJ 0} •H G 1 o +J 1 13 rH rH fO X G G 03 •H tn QJ 01 -rH M rH 01 X fO -P E rH QJ rH rH •H QJ QJ rH •H -H U U rH ra U rH U rd rd X! U u P X! X! 03 3 P C/3 w 2 < QJ 03 •H O C 03 e u r* rd QJ CU O -P I r* rd 0) Pm o QJ PQ 13 CQ 13 CQ O ^f kO rH CN + in + cq 13 • n ro + x 4-> •a •H > 13 G rd X! O QJ 13 •H > N r* CN CQ 13 CO + X +J 13 •H ■a c rd x o QJ 13 •H > N X O o cr. CQ 13 in ro + X 4-> •a •H £ 13 G ro X O QJ 13 -H > N O in 13 P 4-> •H rH a e ro c >1 03 o +J 13 QJ U G 0J U QJ M-l QJ rH H CQ 13 CN + 03 U QJ P G QJ to id QJ u o c •H QJ tP G (d rH •H e fd G >i 13 O QJ 73 •H > * 22 Information Bandwidth and Ground Station Filtering The original Scanning Radiometer was designed with a baseband, video bandwidth of 900 Hz for the visible channel (Modulation Transfer Function (MTF)) equal to or better than 0.15 at 175 cycles/radian) and 450 Hz for the infrared channel (MTF equal to or better than 0.22 at 90 cycles/radian). However, to optimize the electronic processing of the signal, the electrical band- width of the signal for the ITOS D through G instruments was in- creased to 1200 and 600 Hz respectively. There has been no basic change in response of the detectors: the effect of the change was simply to permit the limited response, higher fre- quency data (and its associated noise) already present in this range to be maintained through the data handling system. The individual users have several alternatives available in e choice of a filter 4 for use wi receiver. 5 These alternatives are the choice of a filter 4 for use with the ground station 1. Keep the 1600-Hz filter already present and used for APT data. The total signal bandwidth will be maintained? high- frequency noise, not part of the SR signal, will also be retain- ed. For those users interested only in receiving a picture for synoptic analysis, this technique should be adequate. 2. Install a 1200-Hz filter. High-frequency noise not a part of the original signal will be removed. Full high-frequency response will be maintained, though noise above the "normal" in- formation bandwidth (900 Hz and 450 Hz) will also be present. 3. Install a 900-Hz filter. Normal visible channel data will be displayed at its full planned resolution; high-frequency noise will be eliminated. It should be noted, however, that noise outside the normal information bandwidth (450 and 900 Hz) of the infrared channel will be maintained, but full high-fre- quency response also will be present. A 4-pole Gaussian filter is recommended. This discussion considers only a single filter for both channels of data since these data are intermingled when received on the ground . 23 4. Install a 600-Hz filter. High-frequency noise not a part of the original infrared channel data will be eliminated. Full high-frequency response for the infrared channel data will be maintained though noise above the normal (450 Hz) information bandwidth will also be present. The high-frequency response of the visible channel will be lost. Signal-to-noise ratio will be enhanced but effective geometric resolution will be reduced. 5. Install a 450-Hz filter. Normal infrared channel data will be displayed at its full planned resolution- high-frequency noise will be eliminated. Those users planning to make quanti- tative measurements from the signal will find this method of filtering probably will provide an optimized signal insofar as ground resolution and effective signal-to-noise ratio of the re- ceived signal are concerned. It must be considered that the visible channel response above 450 Hz will be eliminated by this filter; the effective resolution will be reduced from two miles to four miles . 6. Install a filter with bandwidth less than 450 Hz. The effective geometric resolution of both channels will be reduced but effective signal-to-noise ratio for both channels will be improved by elimination of noise. In each case, the filter it- self should be of the 4-pole gausian type to provide an optimum output to the user. VERY HIGH RESOLUTION RADIOMETER The Very High Resolution Radiometer (VHRR) is a two-channel scanning instrument sensitive to energy in the visible spectrum 6 0.6 to 0.7 p,m and the infrared (IR) window 10.5 to 12.5 y,m. As in the Scanning Radiometer (SR), energy is gathered by a 12.7-cm (5-inch) eliptical scan mirror with a ^plane surface area of 100.4 cm 2 (15.6 in. 2 ) and a telescope. The scan mirror is set at an angle of 45° to the scan axis and rotates at 400 rpm. A Dall-Kirkham optical system focuses the incoming radiation at a point behind the primary mirror; the visible energy is detected by a silicon photo diode detector located at this focal point. 6 This range may be expanded for later instruments 24 A dichroic beam splitter reflects the IR radiation which comes to a focus in the plane of a field stop which, together with the detector size defines the channel f ield-of-view. Relay optics are used to re-image the IR radiation on a mercury-cadmium- telluride (HgCdTe) detector. Bandpass filters in both channels define the spectral characteristics of each. The instantaneous field of view is designed to be 0.6 milliradians for both chan- nels; this provides a spatial resolution of approximately 0.5 n.mi. (0.9 km) at the subpoint. The infrared detector is cooled to its operating range (near 105°K) (-270°F) (-168°C) by a radiant cooler. A relatively large cooling patch provides the cooling capacity to bring the detector below the temperature 105°K (-270°F) (-168°C) which provides desired signal-to-noise ratio. Thermostatically con- trolled heaters then warm the detector and maintain the desired temperature. A special labyrinth baffle protects the detector from ice (which has been known to form from outgassing moisture at these low operating temperatures) . The cooling patch itself is suspended on Kapton belts to minimize heat conduction between it and the remainder of the radiometer. In a manner similar to that used for the Scanning Radiometer, the zero point for detected energy is restored to a pre-set zero level once each scan, while viewing space. The output of the radiometer during the remainder of the scan is equal to the dif- ference in detected energy between space and the radiating sur- face (earth) . As with the SR, the anti-sun side horizon will be well defined, providing a zero radiance level for calibration purposes. The sun-side horizon will probably be of indetermin- ate level as the radiometer scans across the solar illuminated target to be used for visible channel calibration. These tar- gets (one for each radiometer) will be illuminated once per orbit as the spacecraft reaches the polar regions. The radiom- eter actually views the 1 earth during approximately 1/3 of the period required for one full mirror rotation. The remainder of the period is given over to viewing space and instrument housing while telemetry and appropriate synchronization data are insert- ed in the data stream. The formatted (discriminated) data out- put for both channels of the ITOS-D radiometer are shown sche- matically in figure 8. Table 10 lists detailed timing informa- tion for these data when combined in a time -sharing multiplex mode for transmission to the ground. 25 IS -J z 7i < o u Li. CO CO Q 2 O u LU CO LU c CO to s U o u o M- r\ n + a O h 1- o — r» t\ + + UJ O UJ o 0) m t£J 2 2 ro z cc w CO m hi 2 III _l _ V) (0 UJ < _l o a. Q a. 2 5 2 a < i- ..i OJ 4 C/3 * V * o Q o o c O o Q LU CC < CC CO u ■H +J CO •H n -p u ro u (TJ (0 G IT •H CO Q) r-\ 42 •H CO •H > C « H I CO c cu cq X > I I • CD CD U tn •H fa tr oo o (N f I tO H o h CO CM cO 3 r» J3 O - i— 1 iH • a. t3 00 8 CO r-l ft) C C CD O r4 ^, O O CI) 0) U m 3 S O * — ' o> 1-1 ill Cm e M CO 4-1 to * ai M 4-1 01 rH iH Cfl 3 00 CO 3 PL, 4J J 1-1 CO CO 1— 1 CO • CD 4-1 CD o CO l-i CO •r4 CO OS CD Ol m •f-l i-l 60 o •o CD > 4J u O iH O •H M vf> r4 4-1 C • ffl u •o i-l •H U 4-1 T> -C l-i 00 N CD 4-1 > CO 4-1 r-l o 4J CD O XI 4-J cfl c 00 3 !-■ u T3 ^J u O CD u a m i-l CD 4J 1-1 u o 0> eg O CD O CO a CO o h u a >> CO • CO X) • a. 4-1 -iH CD > 4-1 CD "4-1 CD a t4 XI e CO ^ 4-1 Cfl B-5 a CO U X> o 5*5 o CO -C a. >> <4-t o . CD o a. O 01 CD 3 O 00 o 4-1 S-S CO CD •0 1-1 I-l o CD C co CN 4J In a. 4.1 CO O vO vX> rH O CD 1 x> CD 4-1 CJ rH 4-1 CD iH • •i-l •i-l CD rH © CO JC O Xi xi § O CO a CO rC3 4-1 rH 5-S XI 6-S 4-1 i-l ro G rH 4-1 3 c I-l ■rH o 3 % 3 CD o cfl o rH u «-* CJ 00 l-i CO rC O 3 B-« o C f-S o CO cfl 4J CD i-l O O >4-l CO 3 1-1 CO 4-1 CD CO Xi u O 1— 1 o (—1 > O 1 CO >4-l 4-1 o 4-1 1-1 r-l !-H ^H o r^ 00 cfl o CD 4J 33 O CO U-l CO CD C >, 03 01 CD J3 CD CD «h CD M HUM I-l r-l CD C CJ > 00 CO .40 CD X> ■a 4J •d •a CO XI B~S 14-1 -tf id T3 a CD XI ••-I 01 a |H X) CO 3 3 3 3 u 3 O vO > 3 i-l XI CO 3 1-1 rH IJ •H XI 3 - 4J 4-1 CD 4-1 4J o 4J w CO • CD 4J 43 c CO 4-1 CD CD 14. 1 3 ^H CD 4J 4-1 1-1 •H tJ 1-1 •■H CD 1-1 > CO > XI rH M C a. I-l a s CD a a. o co o ? § 3 EH Cfl CO CD CO 1 Xi CD 3 O iH « < < < CO < r-l > 4-1 I-l CO < CJ CO 4-1 CM Z < 4-1 00 o 00 o o o XI T) Jd CD Ai OJ CJ rH CJ ^1 o rH o ^1 ^H O I— 1 U CJ M 4-1 4J 4-1 c •!-' c o o o o *5 CJ z o o 00 XI ^ CD O rH O rH XI •H c pel ?s co Ci CO CJ o *w» •iH iH i— 1 o M M g, o ■— I M C a i-H i-H Cfl 4J •H Pu 3 s c rS S-. a Cfl Cfl CJ CD 4J V4 rG iH Pm Cu CO CO CO CO CO o 00 o o 4J CO 4-1 o o 1 1 CJ CD r4 c CO IH c o -*: CO CO rQ JO CO CD CD CJ Cfl 3 |j CO C o c o 3 3 00 r^ C 4-1 h 3 CD O I-l >% cfl CD J3 CO CO CD CO J3 cfl o 1 iH lb co oa CJ 4-1 O 4-1 iH •* X CD 0J 4-1 CO U 4-1 XI CO i— 1 CO XI o IH U CO o. CO CO c a O iH CO o a. Ol r'i co W rH CN CO > > aJ ro 27 T3 a G •H -P C o u I o X! (TJ E-" a x: 01 e • u XI 01 CO &"8 o o U-l t-i t-i cu CO O 0) 4J 00 x; ID c -o 4-1 i-i ^-\ T-I CO c 3 ■^ 5 s ? U h CO O 01 o 01 3 C CO CO ai S-i CO X! h 3 3 ~-t o > 00 Xi CU o o T-I .—i CD a) CU XI XI CO 1 ^H 4J x: 3 CO CO ,— 1 u u t-i -H N-* u-i CU 00 U CU Cu -4- CO l-i 4J CU C 4J 3 cu o < O c 3 a] e o 5-S O O H cu oi 3 3 a < Q. < a, < o o .— i .A 1 > CO CO »£ CU CO l-l 4J CO CO 3 cr oi • cu N -3 33 O -W U1 r-l • O. CN B ^-1 CO to c 00 cd c CO CO c ^ CO CO c > 00 3 >> CU CU T~-{ 6 a. CO CO C/l OI < u-i 00 u-i oo co o vO vD u-i U1 CN CM u-i pH u-i 00 00 r^ 00 O O .— i O CN -a ^ cu o ^ o —l ^H O vO CN vO O >-i u-i r— 1 u-i 4J CN u-\ CN 4-1 C o o z o o o CN oo cj\ ^* 00 • CI c^ O U-l O CN 00 o ci OI CI > h CO CJ ^ CO o 1-4 Cu 3 O C x; 04 a, CO 4-1 4J o 1-1 C CJ -Si CO CO H o c CJ CU CO h >» CO DO •H a T-I C a) g n 0) u XS 4-J B*2 -u o U O •1-1 CO 01 O 3 1-1 > r-4 a) o >. X! •1 O 00 -M i-i 3 CO a) cO CO CO CO CO CO 0) u 01 C c C a c C C c t-i -H CO O 00 00 00 00 00 00 00 00 00 CO U r-H i-l 1-1 1-1 1-1 •H T-I T-I 1-1 i-l 1-1 a CO « 4-1 CO CO CO CO CO CO CO CO CO 00 > a 1-4 B*-? 0) oS oS OS OS OS OS os OS os CO 0) O T-I I-H I-I M M I-I I-I I-I i-l M 3 CO CO CO 09 CO CO CO CO CO -J CO CO CO CO CO CO CO CO CO CO •i-i • 01 rH R-8 1-1 0) CO co CO CO co CO co co co 0) a a -a O H o C) co 11 I-l 01 3 a CJ 01 u 0) PL, a CO 4-1 CO * O t-i r-H O 4-> a o o z o .M 0) CJ --I O -I r-l O CJ In 4-1 4J C O O Z O o o o o -3- co o oo o ■a £• a) CJ -H O rH -•h o o >h 4J 4-> C o o z o O r-l ■-I o CJ M 4J 4-> C o o Z CJ jj h M CO 0) 0) 0) JrJ -M U U 4J a a CO O a. CJ CJ v-^ C C >> f-. c co i co CO C) X XI CO 3 3 75 CO 01 o 4-1 T3 CO CO e Q, 00 o o ccl CO a a a a OO 00 oo C4 OS OS 1 01 a § CO CO CO CO to CO U"l 00 i— i in m ct\ -J- O •-O CTN 01 c c 00 o o M T-I M h u 1-4 CO 4J o o o 4-1 4-1 CO CO 00 CO CO >-i c c c I-l • Xt 0) V 01 Xi X i-l CO /—. CO ^-N CO 1-1 1-4 i-4 4-> o o s-\ .-4 i-H CO 0) 0)0 0)0 01 u CO CO CJ 00 >-< vf t-l --4 MO CJ CJ u 3 ro 3 CN 3 oo 01 CO 4-1 *-• + *-• + V 01 CJ 4J CO CO CO 00 1— 1 C U 4-1 1-4 O u o CO Xt 01 s-s 01 0) 4-1 0) 4-1 4J 1-1 t4 P. o Q. o. 1— 1 CO T) o a cn 6 i- a ^o o 1-4 CO o 01 + 0) + 0) 1 > > OS en H --' H --' H »-' CO c 00 CO N i-l c o I-l XI CJ c >- cm. o X! CJ S-4 o o_ o co oa 4-1 d) a x o 0) N P. >, MH i-l 4-1 O 3 co £ CO 01 > o xi CO x 4J r-l CO CO 0) V4 >-i o CO u 3 t-i O- 0) N i-H S 2 i oo o o °t 0) • -i c o >>o O CT. r- 0) C 4-1 O CO CO 4-1 I-l C CJ 3 ' O o co a D- O < co z 29 For recording on the spacecraft tape recorder (capacity is only 8^ minutes of data) and for real-time (High Resolution Picture Transmission (HRPT) ) to the ground (S-band at 1697.5 MHz) the output of the two ^radiometers will generally be com- bined in a "time-sharing" mode. Bandwidth limitations and the desire to maintain signal-to-noise ratios preclude using the simultaneous output of a single radiometer except for backup purposes when degraded data would be acceptable (see figure 9) . Since only limited recording capacity is practical because of the high data rates and volume, it is not possible to format the data for direct transmission by playing back one channel from the recorder as is done with the Scanning Radiometer. In the primary mode of operation the two VHRR instruments are slaved together but are exactly 180 degrees out of phase. While radiom- eter no. 1 is viewing the earth, no. 2 will be looking upward at its housing. By proper electronic switching, it is possible to transmit first the infrared channel data from one radiometer, and then, one-half mirror rotation period later, the visible data from the second. It should be noted that the data from the two channels will not be coincident; some offset (about 5 n.mi. (8 km) on the earth at the contiguity point) will exist. Pre- launch alignment measurements will provide an indication of the degree of non-coincidence ; these figures can be used to correct for offset when gridding the pictures after receipt. These cor- rections can reduce the coincidence uncertainty to less than 2 n.mi. (4 km) . Total location inaccuracy, when considering space- craft attitude as well, should be less than 1/3 degree of lati- tude, or 20 n.mi. (37 km) . In the event of the failure of a single VHRR instrument, two backup data transmission techniques will be available. The simplest selection will be to transmit data from one channel only. Data format, transmission, and signal-to-noise ratio would then be unchanged. In place of data from the other chan- nel, backscan information would be transmitted to complete the time for a full mirror rotation. The second alternative in- volves a loss in effective signal-to-noise ratio. In this alter- nate method, data from both channels of the single operating instrument are frequency multiplexed and transmitted. Should a 7 The output from one channel of radiometer #1 will immediately precede the output of the alternate channel from radiometer #2. Each output is present during one-half the period necessary for one mirror rotation. 30 single instrument fail, a choice of backup mode will be made after a thorough analysis of user needs and requirements. VHRR Performance VHRR data can be used in the same way the SR data are used. The infrared channel output can be used to determine the equiva- lent black -body temperature of the radiating surface. The noise equivalent differential temperature (NEAT) as measured at the instrument output is estimated to be 0.5 C ( 0.9°F) for a 300°K (80.6°F) (27°C) scene and 2.0°C (3 .6°F) for a 185°K scene. These values will be degraded by the transmission, receiving, and data processing equipment. In the normal time-sharing mode of operation at a local station the NEAT for a 300°K scene is expected to be approximately 1^° to 2°C, for a 185 K scene, 6° to 8°C. In the backup mode of operation, in which data from both channels are frequency multiplexed, the NEAT will be de- graded to 4° to 5°C for a 300 K scene and 20° to 25°C for a o 185 K scene. When tape recorded and analyzed centrally, the NEAT is expected to be degraded somewhat over that received di- rectly without recording. For a 300°K scene NEAT is estimated to be 2° to 3 U C; for a 185°K scene, 12° to 15°C. Here again, sta- tistical processing of temperature data from a relatively uni- form radiating surface should reduce the uncertainties to some extent (perhaps by a factor of 2) . VHRR - High Resolution Picture Transmission (HRPT) System In the primary mode of operation (time-shared transmission of IR data from one VHRR and visible channel data from the second) the composite signal frequency modulates a 99 kHz subcarrier ((figure 9). In the backup mode of operation, where the two chan- nels of data from a single radiometer are frequency multiplexed, the output from one of the channels will modulate the 99 kHz subcarrier while the output from the other modulates a separate 249 kHz subcarrier (table 11) . In either mode of operation, the modulated subcarriers will, in turn, frequency modulate one of the two redundant 1697.5 MHz S-band transmitters to produce a RF carrier bandwidth of 1.0 MHz. In the primary mode, a deviation ratio of about 2 will be employed, while in the backup mode, deviation ratios of 1/3 to 1/2, will be used, respectively, for the 99 kHz and 249 kHz sub- carriers. The output of each transmitter will be permanently connected to its own antenna. The radiated wave from either will be right-hand circularly polarized. Sample link calcula- 31 N X N fO CD CO CvJ CO CO o lO ro CO •—1 >-x x ! N X i 1 1 O c c r< > > O O CO ° c I N O I ro to CO r-- CvJ 9 £ CM > O CO CO LO CO ro CO 00 CO CO CO o LO ro o o ro O O CO c^ o ro o in LO N0I1VIA3Q U3IUUV0 N0I1VIA3Q cJ3mdV0 UJ o c UJ Q o x UJ a: x < o 00 UJ Q O CO >: Ul x < 00 CO I o o < - 00 X ro U +> u CD (^ CO C •H +) ro rH 'D O e a CD g •H +J I ro CD c ro X! I W ; i CO CD n en •H — CM ro 32 tions are given in Tables 12, 13 and 14. HRPT Receiving Stations At the local HRPT stations, the S-band signal will be received by an appropriate antenna and demodulated by the FM receiver as described in the next section. The subcarriers will then be individually demodulated by FM discriminators to recover their video basebands for recording on an appropriate display device. Antenna-Receiving System 8 It is desired that the antenna-receiver system provide a carrier-to-noise ratio of at least 13.5 dB, and preferably more, to ensure a good operating margin. In designing the ground sta- tion an analysis should be made of the system to show that the desired carrier-to-noise and signal-to-noise ratios will be met. The analysis should consider: (a) Antenna gain and efficiency, (b) antenna noise temperature; this could be assumed at 70°K (-203°C) (-333. 4°F), (c) polarization loss, (d) feed assembly loss, (e) preselector filter loss, (f) preamplifier gain and noise temperature, (g) frequency converter and noise temperature, (h) cable loss, and (i) receiver noise temperature. The antenna should have an autotrack capability and be design- ed to receive right-hand circularly polarized signals from the spacecraft. The system should be designed for continuous track- ing of orbital passes from any azimuth direction with elevation angles down to 5 degrees above the local horizon. It may be desirable to provide for remote control of the antenna up to 1500 ft (457 m) depending upon the particular installation) . The remote control unit should include azimuth and elevation indicators, autotrack/manual selector, velocity and position controllers and manual hand cranks and braking mechanisms on both axes. It is recommended that a parametric amplifier be used as the preamplifier and that it and the frequency converter 8 Compiled by D. Holmes and A. Vossler, NESS, Ground Systems Group . 33 be mounted on the antenna structure close to the antenna feed. Sufficient gain should be provided by the frequency converter to overcome cable losses between the antenna and the receiver. The receiver should be of high quality, having a noise figure of no more than 10 dB. A highly stable, switchable Automatic Frequency Control (AFC) circuit should be incorporated. Select- able Intermediate Frequency bandwidths of 50, 100, and 1000 kHz and perhaps others should be considered. The filters could be in plug-in module form. The filters should provide for inter- channel separation in the backup mode of at least 20 dB, assum- ing the signal power to be 10 dB down at the 163-kHz and 185-kHz pass-band limits and signal power roll-offs of 40 dB per decade above and below these frequency limits. Consideration should be given to providing auxiliary outputs at the analog video and first FM demodulator for tape recording purposes. The ground station equipment is listed in table 15; the block diagram for the ground station is shown in figure 10. 34 Table 11. — VHRR HRPT real-time mode characteristics Frequency Transmitting power output Transmitting circuit losses Antenna directivity- Antenna polarization Carrier modulation Peak carrier deviation normal submode backup submode (IR only- 1 subcarrier) backup submode (IR & visible 2 subcarriers) RF Spectrum bandwidth normal submode backup submode (IR only- 1 subcarrier) backup submode (IR & visible 2 subcarriers) Subcarrier center frequencies normal mode backup submode (IR only- 1 subcarrier) backup submode (IR & visible 2 subcarriers) Subcarrier modulation Peak subcarrier deviation Baseband video bandwidth 1697.5 MHz +0.005% 5 watts min . 0.7 dB maximum +1.9 dB minimum at 5° elevation Right hand circular FM - 300 +47 kHz 300 +47 kHz 187 +30 kHz 0.9 MHz 0.9 MHz 1.0 MHz 99 +1.4 kHz 99 +1.4 kHz 99 +1.4 kHz 249 +1.2 kHz FM +29 +2.4 kHz 35 kHz 35 Table 12. — VHRR-HRPT real-time S-band link analysis (general) Contribution element Gain Spacecraft transmitter power (5 watts) 37.0 dBm Spacecraft transmitter circuit loss (estimated) -0.70 dB Spacecraft antenna gain 1.90 dB Pointing loss 0.0 dB Path loss (range 2180 miles; elevation 5°) -169.2 dB Polarization loss -0.6 dB Receiving circuit loss -1.00 dB Off beam loss (receiving pointing loss) -0.50 dB 36 Table 13. — VHRR-HRPT real-time (S-band) link analysis (detailed) Paraboloidal Reflector Parameter 15 foot 10 foot Receiving antenna gain Total received power 35.7 dB -97.4 dBm 32.0 dB -101.1 dBm Received noise spectral density -174.3 dB/Hz -174.3 dB/Hz (System temperature 269K) (-147.3 dBm/Hz) (-147.3 dBm/Hz; Received power noise spectral density 76.94 dB/Hz 73.3 dB/Hz Received noise power IF bandwidth : 1MHz Carrier to noise ratio -60.0 dB (-114.3 dBm) 16.94 dB Baseband signal to noise ratios (Peak to peak/rms) Normal mode (99 kHz) 49.3 dB Backup mode (frequency multiplex) (99 kHz) 33.7 dB (249 kHz) 34.5 dB -60.0 dB (-114.3 dBm) 13.3 dB 42.2 dB 27.5 dB 27.4 dB 37 Table 14. — Signal-to-noise ratio for VHRR HRPT real-time S-band link , worst case analysis Contributing element 15' Antenna 10' Antenna VHRR sensor VHRR processor S-band transmitter RF link Normal mode 43.7 dB 48 dB 48 dB 49.3 dB Backup mode (frequency multiplex) 34 dB Ground receiver (estimated) 48 dB Demodulator (estimated) 50 dB Overall system Normal mode 40 dB Backup mode 30 dB 43 .7 dB 48 dB 48 dB 40.0 dB 24.9 dB 48 dB 50 dB 37 dB 25 dB 38 Table 15. — VHRR-HRPT real-time ground station equipment Item Characteristics Antenna Type: Parabola - tracking Size: 10 to 15 feet (diameter) Polarization: Right-hand circular Pre-selector loss: 1.0 dB maximum Preamplifier Type: Uncooled paramp* Noise figure: 1.3 dB maximum (101°K) Gain: 17 dB minimum Re ce ive r Type : FM with mean-of-peaks AFC IF bandwidth: 1.0 MHz Noise figure : 10 dB maximum Demodulator Type: 2 FM subcarriers Bandwidth: 140 kHz (e^ach subcarrier) Baseband output bandwidth: 35 kHz *A cooled parametric amplifier is suggested for use with the 10-foot antenna to maintain a reasonable margin. 39 _J uj tr z u z o Q < UJ or x Q o o - o > UJ cu u 6 (U ■H co +J 3 1 1 rH iH ro 03 0) U P iH H !-H a (0 n u i •H K & 3 Eh 1 > 0) u 40 Operational Limitation The 1697.5 MHz transmitter used for global VHRR data trans- mission must also accommodate all transmission of recorded data to the CDA stations (Wallops Island, Virginia or Gilmore Creek, Alaska) . During tape recorder playback to the CDA stations, the VHRR data, though remaining in the same frequency domain, are fre- quency multiplexed and are broadcast with insufficient power density (carrier deviation reduced to 55 kHz) to provide usable data to VHRR stations within range of the spacecraft. Usable data will be acquired only by the 85-ft. antenna at the CDA station. VERTICAL TEMPERATURE PROFILE RADIOMETER The Vertical Temperature Profile Radiometer (VTPR) is an in- strument designed to measure infrared radiance in eight narrow- band spectral regions between 11 and 19 micrometers. These data can be used to deduce the atmospheric temperature profile of the radiating column. Sensors (channels) in each of the six spec- tral intervals of the carbon dioxide absorption band (table 16) will measure energy from a different range of altitudes in the atmosphere; the atmospheric temperature profile will be deduced from these measurements. Channel #1 (668.5 cm~l) , the Q branch, is a maximum absorption region. All energy in this wave number that reaches this layer from below will be absorbed and re- radiated upward. The CO2 acts as a black body at the tempera- ture of the layer. Thus, data from this channel can be used to determine the temperature near the top of the atmosphere. Other channels receive their energy from lower levels because the lay- ers of the atmosphere above the radiating layers are reasonably transparent to this energy. Data from the water vapor channel (535 cm"-'-) are used to correct readings in other channels; data from the window channel (835 cm - l) are used to determine surface temperature in clear areas and to indicate cloudy areas. In cloudy areas, temperature profiles can be computed upward only from the cloud top level. The VTPR instrument (figure 11) is equipped with a single optical system and a pyroelectric detector. A wheel with the eight filters that define the channels is located in the opti- cal path In front of the detector. This wheel rotates at 120 rpm, bringing each of the eight filters into the field of view every 62.5 milliseconds. By this method, the data from which a 41 o O 1— z z: Ll) z h- ^£ o Zh- z° pec Ouj Sd ^Li_ ^1 — : nr \ or o o -p c (U ^-^ 6 >. 3 c M fD -P a W e C •H u PS Cn ^ C •H > P, 0> IW 0) c •H S tn o> C ■H W > CO U cu •H C M M •P ITJ OJ PQ a m w H 1 >i 1 w • 0) ■H +J rH ^1 D 0» o U u 3 — tn •H fa 42 temperature profile may be deduced is obtained every 0.5 seconds, The instrument scans across and 31.45 degrees to either side of the orbit path in 23 equal steps; coverage along the satellite track results from the movement of the satellite. The scan and satellite motion combined provides essentially global coverage except in the equatorial region where there are gaps in cover- age between successive orbits of the satellite. The instrument field of view (2.235 by 2.235°) provides a ground resolution of approximately 32 n.mi. by 32 n.mi. (59 km by 59 km) at the subpoint (figure 4). Thus, one complete scan of 23 steps sweeps across an area approximately 32 n.mi. (59 km) wide by 736 n.mi. (1364 km) long. The time to complete one scan is 12.5 seconds, one second of which is used for the scan mirror retrace prior to starting a new line of data. The VTPR is designed to have an absolute accuracy better than 0.5 percent and a relative accuracy between channels of 0.125 percent (0.25 percent for the Q branch). To achieve this level of accuracy, it is necessary to calibrate the instrument at fre- quent intervals. Calibration is used to check the absolute radiance calibration and linearity cf the instrument. For cali- bration, the instrument first looks at space (4°K) for 16 sec- onds and then at an internal black body source approximately 285°K (12°C) (53.6°F), for 15 seconds. Telemetry data necessary for data interpretation is inserted in the data stream during the "flyback" (fast scan retrace) period and during calibration periods. To maintain the signal-to-noise ratio of the instrument through the data processing and transmission link, the instru- ment analog output is digitized (to 10 bits) before storage on the spacecraft recorder. The signal from the detector is fed to an integrator which optimizes the system signal-to-noise by accurately measuring the data leve] of the input. From the in- tegrator the signal goes to a Buffer Amplifier which brings all the signals to a common baseline and raises the level of the Q branch data by a factor of four to make the best use of the digital range. This step is necessary because of the limited response in this narrow-bandwidth channel. Though radiometric accuracy is not improved by raising the signal level, the quan- tization error (+0.5 bit) is limited to the same percentage as that present in data from other channels. Finally, the data are digitized and formatted with appropriate telemetry for stor- age on the spacecraft recorder. 43 Table 16. — VTPR spectral filter characteristics Channel Wave Numbe r Bandwidth Region 1 (Q branch) 4 6 7 8 668.5 cm 695 725 535 835 747 708 677 -1 7.0 +0.5 cm 10.0 +2.5 1.0.0 +1.0 -2.0 10.0 +1.0 -2.0 8.0 +1.0 -2.0 10.0 +2.5 10.0 +2.5 10.0 +2.5 -1 CO- CO^ CO- Water vapor IR window CO. CO- CO. 44 Data from this instrument are not available for direct trans- mission to local stations and can be acquired only at the CDA's, which retransmit them for central processing and analysis. SOLAR PROTON MONITOR The Solar Proton Monitor (SPM) measures the flux of energetic particles (protons, electrons, etc.) in several energy ranges. The SPM is used to detect the arrival of energetic solar protons in the vicinity of the earth. The SPM measures the energetic particle flux in several ranges: protons in the 10-, 30- and 60-Mev range, and electrons in the 100- to 750-Kev range. The flux toward the earth along the local vertical is measured with one set of detectors. A second set of detectors measures the flux along the orbit normal from the side of the spacecraft away from the sun. The data are tape recorded in digital form and are transmitted to the ground, when higher priority 9 data are not present, by modulation of the ITOS beacon transmitter signal. The tape-recorded data are quickly processed at NESS after re- lay from a CDA station. A greatly reduced volume of processed data is sent to the NOAA Space Environment Laboratory at Boulder, Colorado, for solar storm warning purposes. Later all the pro- cessed data are sent to Boulder for study and archiving. 9 Attitude scanner signals, spacecraft telemetry, etc. 45 Sxl COPY U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration Rockville, Md. 20852 APPENDIX The Secretary-General December 28, 1971 World Meteorological Organization 41, Avenue Giuseppe Motta Geneva, Switzerland Dear Mr. Secretary-General: Your letter of 14 October 1971 (25.747/OSM) solicited clari- fication of plans for automatic picture transmissions from U.S. operational meteorological satellites. We regret that uncertainties apparently continue to prevail. The following is a summary of the main points regarding our plans for the direct broadcast of images. 1. The Automatic Picture Transmission (APT) service, defined as the direct broadcast of images in the very high frequency (VHP) band (137.62 or 137.5 MHz), and having a resolution on the order of three km, will be continued in- definitely. However, the sensors used to obtain the images may be changed or modified from time to time. We expect that such changes will require only minor modification to existing APT receivers. 2« As was announced several years ago, a most import- ant modification of the APT service will be the introduction during 1972 of satellites (ITOS-D and later satellites) carry- ing only scanning radiometers for direct broadcast. The use of scanning radiometers, (similar to those used on ITCS-1 and NOAA 1) will be continued in the future so that APT ser- vice will be available at night as well as in the daytime. 3. APT broadcasts of signals., generated by vidicon cameras will continue (depending upon user requirements) as long as old satellites equipped with such cameras continue in working condition, and should provide a period of transi- tion to complete reliance on scanning radiometers for APT. Therefore, an optimum configuration for APT recorders during this period would be that which retains the option to display data generated by either the vidicon camera or scanning radi- ometer. Ultimately, only scanning adiometers will be used to generate images for the APT serNice. 46 COPY 4. When only scanning radiometers are used to generate images for the APT service (as will be the case with the ITOS-D and subsequent spacecraft in polar orbit) , both visible and infra- red channels will be broadcast simultaneously during the daylight portion of each orbit. Depending on the design of present APT receivers, they will need little or no modification to receive and display both channels. To our knowledge, all existing APT receivers can be used to display, at a minimum, one or the other of the two channels without any modification. 5. The Very High Resolution Radiometer (VHRR) , to be flown on the U.S. operational meteorological satellites in polar orbit (ITOS-D et. seq.) beginning before the end' of 1972, is entirely unrelated to the present and planned APT service. The VHRR will be used in a new broadcast service, to be called the "High Reso- lution Picture Transmission" (HRPT) service, and will be operated separately from, but simultaneously with, the APT service. In summary, there will be two independent cloud imaging direct broadcast services which will be operated simultaneously . The first will be the continuation of the APT service on VHF which will require a slight modification to those APT displays not al- ready modified for scanning radiometer compatibility. The second service to be introduced in 1972 is the HRPT service which will broadcast on an S-band frequency (1697.5 MHz) and have a resolu- tion on all channels of about one km. Initially we will use the VHRR as an imaging sensor, with both visible and infrared chan- nels being broadcast, in the HRPT service. This second system will require an entirely new ground station because of the high resolution and associated bandwidth. This ground station, of course, is much more sophisticated (and expensive) than that required to receive APT data. We understand that there is considerable concern among some mem- bers having APT ground stations regarding the proper display of APT signals originating from the new scanning radiometer sensor. We shall be happy to assist members and the suppliers of their display equipment in finding solutions to this problem. Anyone wishing to obtain such assistance, or more detailed information on the ground equipment for the HRPT service, may communicate with the Director, National Environmental Satellite Service, National Oceanic and Atmospheric Administration, FOB-4, Washing- ton, D. C. 20233, USA. Requests for assistance on APT problems should include specific information concerning the display device 47 the user has in service or contemplates using. Some more de- tailed information concerning APT and HRPT ground station require- ments will be forwarded soon in a supplement to this letter. You may wish to circulate this letter for the information of members . Since re ly / /s/ Robert M. White Permanent Representative of the US to the WMO Enclosures «U.S. GOVERNMENT PRINTING OFFICE 1972— 481-332/209 I 48 . (Continued from inside front cover) NESCTM 20 Mapping of Geostationary Satellite Pictures - An Operational Experiment. R. C. Doolittle, C. L. Bristor and L. Lauritson, March 1970. (PB-191 189) NESCTM 21 Reserved. NESCTM 22 Publications and Final Reports on Contracts and Grants, 1969--NESC. Staff Members, January 1970. (PB-190 632) NESCTM 23 Estimating Mean Relative Humidity From the Surface to 500 Millibars by Use of Satellite Pictures. Frank J. Smigielski and Lee M. Mace, March 1970. (PB-191 741) NESCTM 24 Operational Brightness Normalization of ATS-1 Cloud Pictures. V. Ray Taylor, August 1970. (PB-194 638) NESCTM 25 Aircraft Microwave Measurements of the Arctic Ice Pack. Alan E. Strong and Michael H. Fleming, August 1970. (PB-194 588) NOAA Technical Memoranda NESS 26 Potential of Satellite Microwave Sensing for Hydrology and Oceanography Measurements. John C. Alishouse, Donald R. Baker, E. Paul McClain, and Harold W. Yates, March 1971. (COM-71-00544) NESS 27 A Review of Passive Microwave Remote Sensing. James J. Whalen, March 1971. NESS 28 Calculation of Clear-Column Radiances Using Airborne Infrared Temperature Profile Radiometer Measurements Over Partly Cloudy Areas. William L. Smith, March 1971. (COM-71-00556) NESS 29 The Operational Processing of Solar Proton Monitor and Flat Plate Radiometer Data. Henry L. Phillips and Louis Rubin, (in preparation). NESS 30 Limits on the Accuracy of Infrared Radiation Measurements of Sea-Surface Temperature From a Satellite. Charles Braun, December 1971. NESS 31 Publications and Final Reports on Contracts and Grants, 1970--NESS. December 1971. NESS 32 On Reference Levels for Determining Height Profiles From Satellite-Measured Temperature Profiles. Christopher M. Hayden, December 1971. NESS 33 Use of Satellite Data in East Coast Snowstorm Forecasting. Frances C. Parmenter, February 1972. NESS 34 Chromium Dioxide Recording — Its Characteristics and Potential for Telemetry. Florence Nesh, March 1972. \ "IP lllllllllllllillllll AQQQ07Z0E2Q3D