t5& 1$ ; S$>(o<0 NOAA TR NESS 6( A UNITED STATES DEPARTMENT OF COMMERCE PUBLICATION / V\ NOAA Technical Report NESS 60 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Environmental Satellite Service Satellite Measurements of Aerosol Backscattered Radiation From the Nimbus F Earth Radiation Budget Experiment H. JACOBOWITZ, W. L. SMITH, AND A. J. DRUMMOND WASHINGTON, D.C. August 1972 NOAA TECHNICAL REPORTS 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. The NOAA Technical Report NESS series is used by these Offices to facilitate early distribution of research results, data handling procedures, systems analyses, and other information of interest to NOAA organizations. Publication of a Report in NOAA Technical Report NESS series will not preclude later publication in an expanded or modified form in scientific journals. NESS series of NOAA Technical Reports is a continuation of, and retains the consecutive numbering sequence of, the former series, ESSA Technical Report National Environmental Satellite Center (NESC) , and of the earlier series, Weather Bureau Meteorological Satellite Laboratory (MSL) Report. Reports 1 to 57 are listed in publication NESC 56 of this series. Reports 1 to 50 in the series are available from the National Technical Information Service, U.S. Department of Commerce, Sills Bldg., 5285 Port Royal Road, Springfield, Va. 22151. Price: $5.00 paper copy; $0.95 microfiche. Order by accession number, when given, at end of each entry. Beginning with 51, Reports are available through the Super- intendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. For Seasons and J. S. Winston and ESSA Technical Reports NESC 38. Angular Distribution of Solar Radiation Reflected from Clouds as Determined from TIROS IV Radiometer Measurements, I. Ruff, R. Koffler, S. Fritz, J. S. Winston, and P. K. Rao, March 1967. (PB 174 729) NESC 59. Motions in the Upper Troposphere as Revealed by Satellite Observed Cirrus Formation, H. McClure Johnson, October 1966. (PB 173 996) NESC 40. Cloud Measurements Using Aircraft Time-Lapse Photography, L. F. Whitney, Jr., and E. Paul McClain, April 1967. (PB 174 728) NESC 41. The SINAP Problem: Present Status and Future Prospects. Proceedings of a Conference held at the National Environmental Satellite Center, Suitland, Md., January 18-20, 1967, E. Paul McClain, Reporter, October 1967. (PB 176 570) NESC 42. Operational Processing of Low Resolution Infrared (LRIR) Data from ESSA Satellites, Louis Rubin, February 1968. (PB 178 123) NESC 43. Atlas of World Maps of Long-Wave Radiation and Albedo -- Months Based on Measurements from TIROS IV and TIROS VII, V. Ray Taylor, September 1967. (PB 176 569) NESC 44. Processing and Display Experiments Using Digitized ATS-1 Spin Scan Camera Data, M. B. Whitney, R. C. Doolittle, and B. Goddard, April 1968. (PB 178 424) NESC 45. The Nature of Intermediate-Scale Cloud Spirals, Linwood F. Whitney, Jr., and Leroy D. Herman, May 1968. (AD-673 681) NESC 46. Monthly and Seasonal Mean Global Charts of Brightness From ESSA 3 and ESSA 5 Digitized Pictures, February 1967-February 1968, V. Ray Taylor and Jay S. Winston, November 1968. (PB 180 717) NESC 47. A Polynomial Representation of Carbon Dioxide and Water Vapor Transmission, William L. Smith, February 1969. (PB-183 296) NESC 48. Statistical Estimation of the Atmosphere's Geopotential Height Distribution From Satellite Radiation Measurements, William L. Smith, February 1969. (PB 183 297) NESC 49. Synoptic/ Dynamic Diagnosis of a Developing Low-Level Cyclone and Its Satellite- Viewed Cloud Patterns, Harold J. Brodrick and E. Paul McClain, May 1969. (PB 184 612) NESC 50. Estimating Maximum Wind Speed of Tropical Storms from High Resolution Infrared Data, L. F. Hubert, A. Timchalk, and S. Fritz, May 1969. (PB 184 611) NESC 51. Application of Meteorological Satellite Data in Analysis and Forecasting, R. K. Anderson, J. P. Ashman, F. Bittner, G. R. Farr, E. W. Ferguson, V. J. Oliver, and A. H. Smith, September 1969. (AD-697 033) NESC 52. Data Reduction Processes for Spinning Flat-Plate Satellite-Borne Radiometers, Torrence H. MacDonald, July 1970. NESC 53. Archiving and Climatological Applications of Meteorological Satellite Data, John A. Leese, Arthur L. Booth, and Frederick A. Godshall, July 1970. (COM-71-00076) NESC 54. Estimating Cloud Amount and Height From Satellite Infrared Radiation Data, P. Krishna Rao, July 1970. (PB-194 685) 56. Time Longitude Sections of Tropical Cloudiness (December 1966-November 1967), J. M. Wallace, July 1970. NOAA Technical Reports NESS 55. The Use of Satellite-Observed Cloud Patterns in Northern Hemisphere 500-mb Numerical Analysis, Roland E. Nagle and Christopher M. Ilayden. April 1971. (Continued inside back cover) WMOS/v r/ WENT Of U.S. DEPARTMENT OF COMMERCE Peter G. Peterson, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator NATIONAL ENVIRONMENTAL SATELLITE SERVICE David S. Johnson, Director NOAA Technical Report NESS 60 Satellite Measurements of Aerosol Backscattered Radiation From the Nimbus F Earth Radiation Budget Experiment H. JACOBOWITZ, W. L SMITH, AND A. J. DRUMMOND c Q WASHINGTON, D.C. AUGUST 1972 UDC 551.510.42:551.508.21:551.521.3:551.507.362.2 551.5 Meteorology .507.362.2 Satellites .508.21 Radiation measuring instruments .510.42 Atmospheric aerosols .521.3 Radiation scattering in atmosphere For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Price 25 cents. CONTENTS Abstract 1 1. Introduction 1 2. Instrument description 3 3. Relation of radiometric measurements to aerosol concentration 5 k* Conclusions 8 Acknowledgment 9 References 9 in SATELLITE MEASUREMENTS OF AEROSOL BACKSCATTERED RADIATION FROM THE NIMBUS F EARTH RADIATION BUDGET EXPERIMENT 1 H. Jacobowitz and W. L. Smith National Environmental Satellite Service, NOAA, Washington, D.C, A. J. Drummond Eppley Laboratory, Newport, R.I. ABSTRACT. Satellite measurements offer a unique opportunity to investigate the backscatter from atmospheric aerosols in parallel with accurate quantitative determinations of earth-atmosphere radiation budgets on both synoptic and planetary scales. This report describes the general character- istics of the instrumentation being developed for this purpose by the National Oceanic and Atmospheric Administration and by the Eppley Laboratory. Also discussed is the possibility of obtaining measurements of the degree of polarization of backscattered radiation in the visible spectrum as part of a future satellite project that could be based upon the Earth Radiation Budget Experiment. These measurements, together with radiation intensity determinations, might permit diagnosing particulate pollutants (aerosols) and monitoring their transport. Simultaneous fixed (wide-angle) and scanning (narrow-angle) integral short -wavelength and long -wavelength outgoing energy flux determinations will permit detailed study of the regional and global influence of atmospheric aerosol pollutants on the heat budget. In 197^ the radiometer is to fly aboard the Nimbus F satellite. 1. INTRODUCTION The Earth Radiation Budget (ERB) Experiment, under current specifi- cations, provides for simultaneous measurement of incoming sun radiation and outgoing earth-reflected short-wave and earth-emitted long-wave radiation by (l) the fixed wide-angle sampling at the satellite altitude and (2) the scanned narrow-angle sampling of the angular dependent radiance components of (1). The integral short-wavelength reflectance and integral long-wavelength emittance of earth will be measured in two ways. The first is an integration Presented as a paper at the American Meteorological Society and Air Pollu- tion Control Association Conference on Air Pollution Meteorology, Raleigh N.C., Apr. 5-9, 1971 Table 1. — ERB solar and earth radiation measurement channels (wavelength, \ , in micrometers, /mi) Solar Earth 0.25-0.30 0.20-14.0 .28- .35 .70-3.0 .30- .1|0 .20-50+ .35- .U5 •UO- .50 .53-3.0 .70-3.0 ,20-U.O .20-50+ over the entire earth' s disc (wide angle f ield-of -view) , to measure the total terrestrial flux passing through a unit area at satellite altitude. The second is a series of measurements by angular scanning (narrow-angle field) of the radiance reflected and emitted from relatively small areas on the earth's surface at a number of zenith and azimuth angles. The scan system has been designed to obtain up to nine different views of a terrestrial area. Knowledge of the angular variation will permit the determination of synoptic scale features of earth's heat budget. Independent in-flight calibration will permit comparison of the two methods. As a result, the outgoing terrestrial flux and the derived radiation budget will be determined on the required synoptic and planetary scales. Regarding spectral subdivision, the solar channels detect radiation flux in seven well-defined wavelength intervals in the ultraviolet and visible regions (table l) , in addition to the (inherently) integrated principal wavelengths of 0,20-h»0 nrrv, and 0.20-^0+ jzin. A major separation is at 0.70 fim (i.e., the visible, near infrared boundary). This is duplicated in the fixed earth reflectance channels, thus permitting isolation of the spectral region where extinction of short-wave radiation by molecular and aerosol scattering predominates in the outward fluxes. Heat budgets will be calculated by means of three complementary techniques. First, by use of the wide-angle (fixed) sensors, the net flux will be obtained directly for the largest area possible from the intended orbit. In the second, statistical samples of narrow-angle (scanning) data will be used to formulate models that describe the angular dependence of reflected and emitted radiation as a function of basic earth-atmospheric radiative features (e.g., background reflection, cloud condition, aerosol concentration, etc.). Heat budgets for local areas will then be obtained by using the angular distribution models in the integration of specific angular measurements of the radiation from these areas. In the third, regional heat budgets will be computed from the scanning radiometer data by integration over complete scans. This comparison of Hocal and regional heat budgets Figure 1. — Design of the instrument pack age for the ERB Experiment (courtesy of Gulton Industries) provides a means for ascertaining the relationships between the radiative fluxes of relatively small geographical areas and those of much larger areas. The global radiation budget will be extracted from the measurements obtained by both kinds of instruments. 2. INSTRUMENT DESCRIPTION The ERB radiometer consists of 22 spectral channels for the measurement of intensities of incoming solar radiation, reflected solar radiation, and outgoing infrared radiation. Measurements will be made within various spectral intervals at angular resolutions sufficient for defining atmospheric outgoing radiative fluxes on synoptic and planetary scales. Figure 1 is a sketch of the ERB radiometer. The nine solar channels, with a conical field of view of 29°, are for observing the solar spectrum within the integral wavelength region of 0.20 - 50+ M m as the satellite orbits over the poles. Simultaneously, various filters for measuring the intensities in the spectral subregions are listed in table 1. This capability is provided to obtain measurements in wavelength intervals in which there is specific interest or in which significant variability of solar emission is believed to occur. Values can be obtained in the following subregions by subtracting measurements obtained at instrumentally fixed intervals :X<0. 53, 0.20-0.53, 0.20-0.70, and 0.53-0.70 M m. In this treatment of data, account will be taken of the small solar radiation increment between the upper wavelength cutoff of the colored glass filtered channels (3.0 /mi) and that of the quartz unfiltered channel (lj..0 M m). A redundant total short- wave earth flux channel (0.20-U.O M m.) normally will be shielded from solar ultraviolet, electron, and proton radiation. It will be occasionally- unshuttered to detect possible deteriorations of the solar channels. Ground commands will be used for shifting the sensors as much as 20° out of the orbit plane to aline them with the sun. Four other earth flux channels will view continuously as much of the earth area as is visible from the spacecraft. These channels will permit separation of the atmospheric reflected radiation into the subregions 0.70 and \>0.70 M m (table l) . As will be shown, these two spectral regions separate the molecular-plus -aerosol from aerosol-dominant spectral contributions to the total backscattered radiation. The total emitted infrared flux (U.0-^n+ um ) will also be observed. A redundant shuttered total earth flux channel (0. 20-50+ M m) is included for degradation detection. The ERB includes four, narrow field-of-view scanning telescopes in a scanning head that alternately measures short-wave (0.2-U.O /mi) and long- wave (k. 0-50.0+ fim) radiation as a result of a beam-splitting chopper. The head will scan in various vertical planes from nadir to horizon, to measure the angular distribution of a reflected solar and emitted infrared radiation from given geographical areas at a variety of solar angles. The instantane- ous fields-of-view of the telescopes are 0.25° x 5.0°, the former in the scan plane. (From a satellite height of 600 n.mi., areas with linear dimensions of 2.5 x 50 n.mi. and 200 x 200 n.mi. are resolved when viewing downward and near earth's horizon, respectively.) The infrared channels will be alined so that they will sight the horizon simultaneously when the scanning head is at the proper nadir angle, to measure the angular variations of the emerging ray at large local zenith angles. These observations are expected to be important as indicators of the amount of backscatter caused by atmospheric aerosols. A black body and a diffuser plate will be included to permit in-flight calibration of the scanning channels. Recent ground observations indicate that the angular distribution of the polarization of scattered radiation may be more sensitive to the aerosol concentration than is the angular distribution of the radiation intensity. For the measurement of polarization, serious consideration is being given to adding four narrow-angle scanning channels to future ERB radiometers. The most important consideration in this complex experiment is that instrument performance at the ground and within the atmosphere be transfer- able to extraterrestrial conditions without significant degradation of signal reproduction, repeatability, and resolution needed for high absolute measure- ment accuracy. In this experiment, the radiometric and readout precision desired in flight operation is 0.1$, with an overall accuracy level approaching 1% in total flux and 2% in spectral flux. Independent in-flight calibration checks to monitor instrumental performance are provided for each of the three measurement programs. 3. RELATION OF RADIOMETRIC MEASUREMENTS TO AEROSOL CONCENTRATION Theoretical computations and ground-based observations of various types of atmospheres are presented to indicate the effects of aerosols upon the radiation to be sensed by the ERB. Three aerosol models were chosen to describe clear, hazy, and very hazy atmospheres. In all the models, a single relative size distribution (independent of altitude) of the particles was chosen- Figure 2 shows the particle concentration at the surface per unit interval of the logarithm of the particle radius r, (dN/d log r), versus log r for the three aerosol models. These concentrations correspond to horizontal visibilities of 23, 5>> and 1 km for clear, hazy, and very hazy atmospheres, respectively. Figure 3 shows the vertical distributions of the aerosol concentrations that were assumed for the models. They were chosen so that the concentra- tions varied exponentially with height in two or more layers. The distributions for the clear and hazy atmospheres are very similar to those used by McClatchey et al. (1971). The vertical distribution of the aerosols for the very hazy atmosphere was assumed to be identical to that of the hazy atmosphere above the 1-km level. Below this level, the concentration was assumed to increase exponentially downward to a surface value corresponding to a horizontal visibility of 1 km. For each of the above distributions, the optical thickness t was computed as a function of the wavelength of the incident radiation, by using the extinction cross sections computed by Zel'manovich and Shifrin (1971) for the size distribution shown in figure 2. The t of a layer of atmosphere is the negative logarithm of the fractional attenuation of the incident beam resulting from absorption and scattering by the aerosols. It is computed by means of t(H) = /" N(h)- ■_ I - N ll r - < X v» ■» i r -■»-■*• i >- LU > > u t/5 /- / / / j i j_ I * 1 h- II- - 1/ - J ~ ~ E y f ~ " -* * 1 - m 1 / >- ll > v / \ I / / - / : ~ M < - o> o u / / /j! / / / u < cula terin — < / / / ^ f / / ^^^ Mole Scat — — — iiu 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 III ii i i i In 1 1 i i i i CN 'o I O lo [%) ssauipiuj pDndQ >o CO 43 & o CO H 0) > fn co rt >o Is H CN 2 CO o pi CD CO rH U O O CD g CN E fc» T3 3. co C — CO CO to 1 ^ o O -H •H -P rC CTJ o -P ^ . — c H CD 03 -p O -P iO •H CO b -P CD O fcuO i co a 1 O -H o • Sh !m o "LA CD CD CO -P -P h Sh cO P o O W)tH ra •H Ft, ( j wo Ql) uo !P 8 S ssoj^ uoijDuijxg 0.80 0.70 0.60 Z 0.50 o 0.40 0.30 0.20 0.10 0.00 -0.10 ~i — i 1 r RAYLEIGH ATMOSPHERE CLEAR SMOG ZENITH ANGLE (< Figure 6. — Degree of polarization of sky- light measured for a clear and polluted atmosphere and as computed for a molec- ular (Rayleigh) atmosphere. The h Q is the sun elevation (after Coulson 1969). An important quantitative indicator of aerosol characteristics is the state of polarization of backscattered radiation, and the dependence of polar- ization on both wavelength and scattering angle. The degree of polarization of backscattered radiation , in the principal plane (i.e., the plate containing the sun, viewed area, and sensor) is proportional to the difference between the squares of the horizontal and vertical vibrations of the electric vector in the plane normal to the direction of propagation of the radiation. Figure 6 is an example of the variation of the angular distribution of the degree of polarization for three atmospheric states and two different solar elevation angles, as obtained by Coulson (1969) with an upward-looking polarizing radiometer. These curves show that the degree of polarization decreases rapidly with increasing aerosol concentration, especially at large solar zenith angles. Similar characteristics are expected in measurements from a satellite-borne downward-looking polarizing radiometer. Although surface reflection, with its attendant polarization, plays a stronger role in the radiation directed outward from the atmosphere than it does for the skylight (thereby complicating the problem of interpretation), the polarization field measured from a satellite should contain retrievable information on aerosol effects. Hence, it should be possible to use scanning radiometer observations of polarization, obtained with ERB-type experiments for diagnosing aerosol concentrations and their horizontal transport over the earth's surface. k. CONCLUSIONS Information on the pollution of the atmosphere by particles and their horizontal transport should be obtainable from satellite measurements of the solar short-wave backscattered radiation. The Nimbus F ERB Experiment is an attempt to measure the critical components of this backscattered radiation, as well as to obtain the outgoing flux measurements with the precision needed for determining the influence of pollution on the radiative balance of the terrestrial atmosphere. It is suggested that future ERB experiments be additionally instrumented to obtain scanning polarizing radiometer observations for the detection of aerosol pollutants. It is proposed that such satellite measurements obtained from the ERB be carefully investigated and, if successful, that full consideration be given to instrumenting operational satellites to obtain such measurements routinely as a means for continued monitoring and evaluating the effects of man's influence on his environment . ACKNOWLEDGMENT The authors wish to thank Prof. K. L. Goulson of the University of California at Davis for his review of this paper, particularly for his special attention to the polarization measurement aspects. REFERENCES Coulson, Kinsell L., "Measurements of Ultraviolet Radiation in a Pollution Atmosphere," Scientific Report No. 1, Department of Agriculture Engineering Grant No. 5R01 AP00742-02, University of California, Davis, Dec. 1969, 62 pp. McClatchey, R. A., Fenn, R. W. , Selby, J. E. A., Volz, F. E., and Garing, J. S. , "Optical Properties of the Atmosphere" (revised), Environmental Research Papers No. 354, AFCRL-71-0279 , U.S. Air Force Cambridge Research Laboratories, Bedford, Mass., May 10, 1971, 85 pp. Penndorf , Rudolf, "Tables of the Refractive Index for Standard Air and the Rayleigh Scattering Coefficient for the Spectral Region Between 0.2 and 20.0 y and Their Application to Atmospheric Optics," Journal of the Optical Society of. America , Vol. 47, No. 2, Feb. 1957, pp. 176-182. Zel 'manovich, I. L., and Shifrin, K. S., Tablitsi po Svetorasseyaniyu (Tables of Light Scattering), Tom 4 (Vol. 4), Gidrometeorologicheskoye Isdatel'stvo, Leningrad, U.S.S.R., 1971, 168 pp. ir V. S. GOVERNMENT PRINTING OFFICE : 1972— 511-317 (35) (Continued from inside front cover) NESS 57. Table of Scattering Function of Infrared Radiation for Water Clouds, Ciichi Yamamoto, Masayuki Tanaka, and Shoji Asano, April 1971. (COM-71-50312) NESS 58. The Airborne ITPR Brassboard Experiment, W. L. Smith, D.T. Hilleary, E. C. Baldwin, W. Jacob, H. Jacobowitz, G. Nelson, S. Soules, D. Q. Wark, March 1972. NESS 59. Temperature Sounding From Satellites, S. Fritz, D. Q. Wark, H. E. Fleming, W. L. Smith, H Jacobowitz, D. T. Hilleary, and J. C. Alishouse, July 1972. PENN STATE UNIVERSITY LIBRARiPc llllllillillllf A0000720lfl3[H