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COMPARING RADIANCES MEASURED BY HIGH SPECTRAL RESOLUTION POLAR ORBITING AIRS AND BROADBAND GEOSTATIONARY IMAGERS Mathew M. Gunshor* 1 1, David 1 Tobin , Timothy J. Schmit 2, 3 and W. Paul Menzel Cooperative Institute for Meteorological Satellite Studies - University of Wisconsin 2 NOAA/NESDIS/ORA/ASPT 3 NOAA/NESDIS/ORA Madison, Wisconsin * [email protected] INTRODUCTION METHODS SUMMARY Purpose Intercalibration Equation IRW Results WV Results • Global applications of weather satellites require a comparison of the various operational instruments. • Geo minus Leo Routine comparisons of NOAA-14 (top) and NOAA-15 (bottom) to 5 operational geostationary instruments. Routine comparisons of NOAA-14 (top) and NOAA-15 (bottom) to 5 operational geostationary instruments. • Radiance validation of new instruments during post-launch checkout provides confidence in instrument performance or could provide an indication of a problem. • Forward model calculated radiances are subtracted from measured mean radiances. GOES-10 Imager IRW Band • LEO = Low Earth Orbiting Instrument (HIRS or AVHRR) Data Collection • GEO = Geostationary Orbiting Instrument • Mean = Measured Mean Radiance in Intercalibration Area • Geo/Leo within +/- 30 Minutes ΔR R GEO R GEO R LEO R LEO Cal Mean Clear Mean Clear • Clear = Forward Model Calculated Clear Sky Radiance Convert to Brightness Temperatures • R = Radiance (mW/m2/ster/cm-1) • Leo within +/- 10 degrees Lat/Lon of geo nadir • T = Temperature (K) • TCAL = Brightness Temperature Difference • B-1 = Inverse Planck Function Conversion From Radiance to Temperature GEO GEO LEO LEO ΔT B 1Mean B 1Clear B 1Mean B 1Clear CAL Spatial Averaging Intercalibration Equation Applied to AIRS • Geo and Leo data smoothed to 100 km (effective resolution) using a moving average. • AIRS radiances are convolved with GEO spectral response functions. • Smoothing and averaging reduces the effects of possible navigation errors and the differences between instrument resolutions. • Spectrally convolved AIRS radiances are compared with measured GEO radiances. • T B -1GEO Mean GOES-8 IRW 42 42 -0.6 K -0.3 K 0.8 K 0.3 K N-14 Delta (geo – leo) Number of THIRS Comparisons TAVHRR THIRS Mean TAVHRR Standard THIRS Deviation TAVHRR AIRS Convolved w/GOES-10 IRW SRF N-15 Delta (geo – leo) Should Differences with AIRS be expected? Number of Comparisons • When AIRS radiances are convolved with GEO spectral response functions, any substantial gaps in the AIRS spectra creates some “convolution error.” The magnitude of this error increases as the gaps in the AIRS spectral coverage increase. Mean Standard Deviation • Convolution error is small in the IRW, but large in the water vapor channel. • In addition to convolution error, other contributions can come from temporal, field of view size and shape, and navigation differences as well as GEO spectral response function uncertainty. -1AIRS Mean -B THIRS TAVHRR THIRS TAVHRR THIRS TAVHRR GOES-10 IRW 353 353 -0.6 K -0.1 K 1.2 K 0.3 K GOES-8 IRW 39 39 -0.1 K 0.1 K 0.9 K 0.4 K GOES-10 IRW 168 168 -0.1 K -0.2 K 1.4 K 0.4 K MET-5 IRW 352 352 -0.8 K -0.4 K 1.1 K 0.6 K MET-7 IRW 424 424 -1.1 K -0.7 K 1.1 K 0.7 K MET-5 IRW 175 175 -0.5 K -0.6 K 1.8 K 1.4 K MET-7 IRW 198 198 -1.2 K -1.0 K 1.1 K 0.7 K GMS-5 IRW 137 137 -0.9 K -0.6 K 1.0 K 0.6 K GMS-5 IRW 40 40 -0.6 K -0.7 K 1.3 K 0.4 K N-14 Delta (geo – leo) GOES-8 WV GOES-10 WV MET-5 WV MET-7 WV GMS-5 WV Number of Comparisons THIRS 237 488 458 327 252 Mean THIRS 1.5 K 2.2 K 3.9 K 3.9 K 1.2 K Standard Deviation THIRS 0.7 K 0.8 K 1.3 K 0.8 K 1.0 K GOES-8 WV GOES-10 WV MET-5 WV MET-7 WV GMS-5 WV N-15 Delta (geo – leo) Number of Comparisons THIRS 119 219 200 0 78 Mean THIRS 0.6 K 1.8 K 3.2 K na -0.1 K Standard Deviation THIRS 1.1 K 1.5 K 1.8 K na 1.7 K • All GEO IRW agree within 1.0 K of LEO IRW on NOAA-14 and NOAA-15 (HIRS and AVHRR). • All GEO WV agree within 4 K of LEO WV on NOAA-14 and NOAA-15 (HIRS). • GOES-10 Imager and AIRS show preliminary differences between 0.1 and 0.3 K. • GOES-10 Imager and AIRS show preliminary differences between 1 and 2 K. • “Convolution Error” between GOES and AIRS is approximately 0.1 K. • “Convolution Error” between GOES and AIRS is between 2 and 3K. • The Mean Radiance inside the Intercalibration Area is calculated from the spatially averaged data. GOES-8 Imager GOES-10 Imager GOES-12 Imager Meteosat-7 • Better intercalibration is possible when operational high spectral resolution instruments cover the entire spectral response function of the broadband instruments. Such comparisons will be vital for validation and monitoring sensor degradation. Meteosat Second Generation FUTURE WORK IR Window IRW Bands Satellite WV Bands TBB (K) TBB from GOES-8 (K) TBB (K) TBB From GOES-8 (K) GOES-8 289.5 N/A 248.7 N/A GOES-10 289.5 0.0 248.9 0.2 GOES-12 289.5 0.0 262.2 13.5 Meteosat-7 288.4 -1.1 257.7 9.0 MSG 289.4 0.1 253.7 5.0 AIRS • More cases will be studied with all operational geostationary instruments. • Convolution error correction methods will be explored. • Additional comparisons will be made with MODIS on Aqua. Routine Intercalibration Water Vapor Channel Sample AIRS spectrum convolved with various GEO IRW and WV bands. Note the gaps in the WV coverage. • New instruments to be added include NOAA-17, MSG, and GOES-12. Acknowledgements • Kevin Baggett, Jim Nelson, and Geary Callan for their programming assistance. Tony Schreiner for providing the background images.