NOAA NESDIS CENTER for SATELLITE APPLICATIONS and RESEARCH GOES-R Advanced Baseline Imager (ABI) Algorithm Theoretical Basis Document For Downward Shortwave Radiation (Surface), and Reflected Shortwave Radiation (TOA) AWG Radiation Budget Application Team Version 2.5 July 30, 2012 1 TABLE OF CONTENTS 1. INTRODUCTION ..................................................................................................... 12 1.1 Purpose of This Document ................................................................................ 13 1.2 Who Should Use This Document ...................................................................... 13 1.3 Inside Each Section ........................................................................................... 14 1.4 Related Documents ............................................................................................ 14 1.5 Revision History ................................................................................................ 14 2 OBSERVING SYSTEM OVERVIEW ..................................................................... 15 2.1 Products Generated ............................................................................................ 15 2.2 Instrument Characteristics ................................................................................. 18 3 ALGORITHM DESCRIPTION ................................................................................ 20 3.1 Algorithm Overview .......................................................................................... 20 3.2 Processing Outline ............................................................................................. 20 3.3 Algorithm Input ................................................................................................. 24 3.3.1 Primary Sensor Data .................................................................................... 24 3.3.2 Ancillary Data ............................................................................................. 26 3.3.2.1 ABI Dynamic Data ............................................................................ 26 3.3.2.2 Non-ABI Dynamic Data .................................................................... 27 3.3.2.3 ABI Static Data .................................................................................. 27 3.3.2.4 Non-ABI Static Data ......................................................................... 28 3.3.2.5 Derived Data ...................................................................................... 33 3.3.3 Grid-level Input ........................................................................................... 35 3.4 Theoretical Description ..................................................................................... 38 3.4.1 Physics of the Problem ................................................................................ 38 3.4.1.1 The direct path ................................................................................... 39 3.4.1.2 The indirect path ................................................................................ 42 3.4.1.3 NTB and ADM conversions .............................................................. 44 3.4.2 Mathematical Description ........................................................................... 48 3.4.2.1 The direct path ................................................................................... 48 3.4.2.2 The indirect path ................................................................................ 51 3.4.2.3 NTB and ADM conversions .............................................................. 54 3.4.3 Algorithm Output ........................................................................................ 57 3.4.3.1 Products ............................................................................................. 57 3.4.3.2 Diagnostic/Intermediate Information ................................................ 58 3.4.3.3 Metadata ............................................................................................ 63 4 TEST DATA SETS AND OUTPUTS ...................................................................... 63 4.1 Simulated/Proxy Input Data Sets ....................................................................... 63 4.1.1 SEVIRI Data ................................................................................................ 64 4.1.2 MODIS Data ................................................................................................ 65 4.2 Output from Simulated/Proxy Inputs Data Sets ................................................ 66 4.2.1 Precision and Accuracy Estimates ............................................................... 67 4.2.2 Error Budget ................................................................................................ 70 5 PRACTICAL CONSIDERATIONS ......................................................................... 73 5.1 Numerical Computation Considerations ........................................................... 73 2 5.2 Programming and Procedural Considerations ................................................... 73 5.2.1 Input Gridding ............................................................................................. 73 5.2.2 Clear-Sky Composite Albedo ...................................................................... 74 5.2.3 Lookup Table Interpolation ......................................................................... 74 5.3 Quality Assessment and Diagnostics ................................................................. 76 5.4 Exception Handling ........................................................................................... 76 5.5 Algorithm Validation ......................................................................................... 77 5.5.1 Pre-Launch Phase Activities ........................................................................ 77 5.5.1.1 Proxy and Simulated Instrument Data ............................................... 78 5.5.1.2 Algorithm Evaluation and Characterization ...................................... 78 5.5.1.3 Product Validation Tool Development .............................................. 80 5.5.2 Post-Launch Phase Activities ...................................................................... 82 5.5.2.1 Product Assessment ........................................................................... 82 5.5.2.1.1 Early Orbit Period ............................................................................ 82 5.5.2.1.2 Long term operations ....................................................................... 82 5.5.2.1.3 Algorithm Refinements .................................................................... 82 5.5.3 Correlative Data Sources ............................................................................. 83 5.5.3.1 Ground-based Measurements ............................................................ 83 5.5.3.2 Satellite Derived Products ................................................................. 84 6 ASSUMPTIONS AND LIMITATIONS ................................................................... 85 6.1 Performance ....................................................................................................... 85 6.2 Assumed Sensor Performance ........................................................................... 85 6.3 Pre-Planned Product Improvements .................................................................. 86 6.3.1.1 Update NTB conversion .................................................................... 86 6.3.1.2 Improve the retrieval over snow/ice surface ...................................... 86 6.3.1.3 Update LUT ....................................................................................... 86 7 REFERENCES .......................................................................................................... 87 APPENDIX ....................................................................................................................... 92 A. Narrow-to-broadband conversion .............................................................................. 92 B. Shortwave spectral bands and corresponding irradiance ......................................... 107 C. Reference surface spectral albedo ........................................................................... 108 D. Dimensions of Angular Distribution Model ............................................................ 110 E. Common Ancillary Data Sets .................................................................................. 112 1. LAND_MASK_NASA_1KM ............................................................................. 112 a. Data description .............................................................................................. 112 b. Interpolation description ................................................................................. 112 2. MDS_L2_CLD_HGT_5KM_FILE ..................................................................... 112 a. Data description .............................................................................................. 112 b. Interpolation description ................................................................................. 112 3. MDS_L2_CLD_MASK_FILE ............................................................................ 113 a. Data description .............................................................................................. 113 b. Interpolation description ................................................................................