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1971028469 0 1971028469-002 ° - 9G45-70 _- USEof GROUND-TRUTHMEASUREMENTS to MONITORERTSSENSORCALIBRATION i i. TECHNICALREPORTNO.16 ' VOLUMEII OCTOBER 1970 CONTRACT NO. NAS 5-10343 ROMEO I_. SABATINI _EOI:_(31: I:_A BC I--I',:'VSK Y prepared for i[ NATIONALAERONAUTANDICSSPACEADMINISTRATION 60DDARDSPACEFLIGHTCENTER i_ GREENBELT,MARYLAND n H [_ ALLIED RESEARCH ASSOCIATES, INC. VIRGINIA ROAD CONCORD, MASSACHUSETTS _H inl nl ,,i, lln llll ii ii ,111 ,ill nnl niH inl i i i i n l i i ii ii • # PRI_EDING PAGE BLANK NOT _LM_ _._. j FOREWORD This report is Volume No. IIof three volumes containing studies of ERTS ,_. Data Management, Dissemination and Processing performed by personnel of ARA "" for the National Aeronautics and Space Administration, Goddard Space Flight Center, ,__ _ ustunddeiesr Conreptroacrtted No.n inNASAlli5-103ed 4R3ese. archThe Awssociork atesdes, cribedInc. her(AeR.inA) isTeanchnicalextensioRneportof tNheo. ': ll, December 1969, entitled "Management, Processing and Dissemination of Sen- ,'i" _ sory Data for the Earth Resources Technology Satellite" by Merritt, et el. The $' current study involved an investigation of the use of ground-truth data to monitor " "_" I ERTS sensor calibrations. This monitoring can be conducted at the ERTS Data _i Center. The authors are indebted to Messrs. E. Merritt and P. Sherr for their review and editingof the report. g. | I r ! I % 1971028469-003 1971028469-004 \ r ABSTRACT The Earth Resource Technology Satellite (ERTS) sensors, i. e., the Return Beam Vidicon (RBV) and Multispectral Scanner (MSS), utilize light energy detectors and associated electronics that may be subject to changes in output for a given scene reflectance. On-board systems for monitoring system response have been provided. However, these monitoring systems are, themselves, subject to change. Additional procedures, therefore, are needed for monitoring of sensor calibration. A survey of potential ground-truth sites and a review of appropriate literature indicate that it will be possible to monitor ERTS sensor calibrations at the ERTS Data Center. Two alternate procedures are defined which will permit judgements to be made with regard to possible sensor degradation or malfunction. The first method, simpler from an analysis point of view, requires the periodic overflight of ground-truth sites by an aircraft with sensor systems similar to those on board ERTS. Such flights should be made concurrent with local ERTS passage. The second technique requires comparisons between radiance values mea- sured by the sensors on ERTS over ground-truth sites and those computed from radiation transfer models using known optical properties of the surfaces at the sites and of the atmosphere. The application of this technique requires repeated on-site measurements of those parameters which are of significance to the radiation trans- • ! fer process. However, it is possible to select sites in which these physical para- meters do not vary significantly in time. For such sites, frequent monitoring of i these parameters may not be necessary. A procedure combining both techniques is proposed. The concept of ground- .: truth sites is central to this procedure and hence ground-truth site requirements are discussed and site selections are presented. Prelaunch and postlaunch data require- ments over these sites are specified. Techniques for the computation of the radiance to be measured over test sites are discussed and sample calculations based on avail- -j able data are presented. The application of these data in real-time sensor calibration -! monitoring schemes is specified in detail. _] ] ] 1 iv le ii i ii / i 1971028469-005 4., I ._ TABLE OF CONTENTS FOREWORD iii '_' | ABSTRACT iv 7_% I LIST OF ILLUSTRATIONS vii _ LIST OF TABLES xi m ! SECTION 1 INTRODUCTION 1 .'- SECTION 2 SUMMARY 2 ": • SECTION 3 EXPECTED RADIANCE AT SATELLITE SENSORS 3 ._} I 3. 1 Spectral Characteristics of the RBV and MSS Sensor :_' Sy stem s 3 _- 3. Z Spectral Reflectance of Test-Site Covers 3 _?" I _. 3.3 Solar Elevation Angle and Atmospheric Optical Y_ I 3.4 STholaicrknessIrradiances and Atmospheric Transmissivities 4 _-, : for "Clean" (Rayleigh) and Turbid Atmospheres 5 _' I 3.5 Method of Calculations 6 3.6 Brief Discussion of Results IZ _ i 3, 6.1 Effects of Turbidity and Solar Elevation Angle lZ I 3.6. Z Effects of Reflectance Variation 14 _. ?' 3.6.3 Relative Contrast of the RBV and MSS Video 14 4 Comparison I 3.7 of the Calculated Radiances to Aircraft Spectrometer Measurements 15 I SECTION 4 4.SENSOR1 AircraftMONITTechnORINGique TECHNIQUES AND PROCEDURES 311 4. Z Modeling Techniques 32 I 4.3 Test Site Selection and Ground Data Collection 33 4.3.1 Test Site Characteristics 33 p I 44,.3.3.3Z POnote-Sntitiale MeGrasuounrementsd-Truth Sites 3437 4.4 Suggested Sensor Calibration Monitoring Procedure 39 _s1 4.4. I Film Calibration Measurements 40 4.4.2 Digital Data Calibration Check 41 1 SECTION 5 4R.5ECODataMMENCDAlassiTIOficationNS File Entries 4443 REFERENCES 45 I APPENDIX A DETAILED DISCUSSION OF MAJOR GROUND TEST SITES 47 A. 1 Smoke Creek and Black Rock Deserts 47 ! V ! ............................................ i i H in ii i i i i iii in 1971028469-006 TABLE OF CONTENTS, contd. A. 2 Great Salt Lake Desert 57 A, 3 Sonoran Desert 64 REFERENCES 74 APPENDIX B REFLECTANCE CURVES 75 REFERENCES 84 APPENDIX C SPECTRAL REFLECTANCE OF TEST SITE SURFACE COVERS 85 C, 1 Semi-Desert and Desert Vegetation 85 C, 2 Soils 87 C. 3 Influence of Weathering on Surface Reflectance 93 REFERENCES 97 1971028469-007 I ! | /. :_ • LIST OF ILLUSTRATIONS I ,i _.,. la Spectral Response for ERTS-A Return Beam Vidicon (RBV) 17 ?'_- lb Spectral Response for ERTS-A Multi-Spectral Scanner (MSS) 17 "'1" 2a Solar Elevation Angles at 9:30 AM at 30 ° , 40 ° and 50°N Latitude 18 Zb Solar Elevation Angles at 10:00 AM at 30 ° , 40 ° and 50°N Latitude 18 !2. 3 Air Masses for Different Solar Elevations 19 _ • 4 Solar Irradiance at the Earth's Surface for DifferentAtmosphere _ I (Rayleigh-Type) Optical Thicknesses 19 _ 5 Solar Irradiance at Sea Level for Different Air Masses for a _'_ • Turbid Atmosphere Z0 ! 6a TransmJ ssion for a RaEleigh Atmosphere at Solar Elevation Angles /" of 90° , 60 ° , 42 ° and 20 ° 21 _ I 6b Transmission for a Dry Turbid Atmosphere at Solar Elevation ._,, Angles of 90°, 60°, 42 °, and 20° with Aerosol Distributionas Shown and 0. 229 cm of Ozone 21 I 7 Transmission of Solar Radiation by Water Vapor 22 _.' •i 8 PatSenhsorof Solar Radiation Through the Atmosphere to the ERTS 22 "_). 9 Specific Intensity of Scattered Radiation from Atmosphere Alone _ I 10 fRoradiVaiewince ngAvatilablhe Naedirto RBV and MSS Channels from Atmosphere 33 Alone (RA) 23 I II Radiance Sensed by RBV at Nadir from Surfaces of 50% and 100% Reflectance - Rayleigh Atmosphere 24 I 17 ReadiaflecntceanceSense- Turbidd by RBAVtmoatsphNereadir fr(2omg/cSmu_");facesmoistuofre)50_0 and 100% Z4 Reflectance - Rayleigh Atmosphere 25 i 13 Radiance Sensed by MSS at Nadir from Surfaces of 50°/0 and 100% 14 Radiance Sensed by MSS at Nadir from _r2faces of 50°/o and 100_/0 1 I Reflectance - Turbid Atmosphere (2 g/cm moisture) 25 15 RBV No. 1.*Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm moisture) 26 I 16 RBV No. 2. Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm moisture) 26 I _ Illll Ill I Illllllllllllillll Ill I[I II I II Illl Ill I I I I I I I " . i 1971028469-008 LIST OF ILLUSTRATIONS, contd. 17 RBV No. 3: Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm = moisture) 27 18 MSS No. 1: Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm _ moisture) 27 19 MSS No. 2. Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm _ moisture) 28 t 20 MSS No. 3: Radiances for Typical Natural Surfaces - Turbid Atmosphere (2 g/cm _ moisture) 28 21 MSS No. 4: Radiancos for Typical Natural Surfaces o Turbid Atmosphere (2 g/cm _ moisture) 29 22 Aircraft Spectrometer Measurement of Solar Reflected Radiation over Gulf Stream at I000 meters (Solar Elevation Angle _-60c) 29 23 Aircraft Spectrometer Measurement of Solar Reflected Radiation over Heavy Fot-estedArea, Big Sur, California, from -_2-I/2 km (solar Elevation is 60°, May 23, 1968) 30 24 Aircraft Spectrometer Measurement of Solar Reflected Radiation Over a Mature Wheat Field, Kansas, from -_2-I/2 km (Solar Elevation _-60°, July) 30 25 Loc=tor Map of Major Test Sites (Courtesy of Jeppesen and Company, Denver) 35 } 26 Display of Reflectance for Each Spectral Band as a Function of Time and Site Location 42 A-1 Owyhee River Area Relief Map 50 A-2 Smoke Creek and Black Rock Desert Area Geological Map 51 I , A-3 Pyramid Lake, Smoke Creek and Black Rock Desert Area Relief Map 52 A-4 Smoke Creek and the Black Rock Desert Area as View by Nimbus I 53 _I A-5 Smoke Creek Desert Area Relief Map 54 -| " A-6 Aircraft View of Smoke Creek Desert Area 55 _J A-7 Aircraft View of Smoke Creek Desert Area 57 71 J A-8 Great Salt Lake Desert Area Relief Map 58 A-9 Great Salt Lake Desert Area as Viewed by Nimbus I 65 ] J ] viii iiiiiin in iii iiin I,HI I f I II I IIII I ,I Inl, II IIII ,11 i I 1971028469-009 • f LIST OF ILLUSTRATIONS, contd. A-I0 Great Salt Lake Desert Area Geological Map 60 A- 11 Structural Map of Northwestern Utah Showing Major Thrust and Tear Faults 51 t A- 12 Aircraft View of Great Salt Lake Desert Area 62 A- 13 Aircraft View of Great Salt Lake Desert Area 63 t A-14 Sonoran Desert and Sand Hills Area Relief Map 68 A-15 Sonoran Desert and Sand Hills Area as Viewed by Nimbus I 69 A-16 Sonoran Desert and Pinacate Volcanic Field as Viewed by ,.