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Anomaly of CRTM BT on the SEVIRI IR3.9 band

-- CRTM Technique meeting --. Anomaly of CRTM BT on the SEVIRI IR3.9 band. XingMing Liang, Alexander Ignatov, and Nikolay Shabanov. Monitoring SEVIRI BT against CRTM: June 2008. In LW bands, SEVIRI M-O Biases are ~ +0.5K & consistent with AVHRR

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Anomaly of CRTM BT on the SEVIRI IR3.9 band

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  1. -- CRTM Technique meeting -- Anomaly of CRTM BT on the SEVIRI IR3.9 band XingMing Liang, Alexander Ignatov, and Nikolay Shabanov

  2. Monitoring SEVIRI BTagainst CRTM: June 2008 In LW bands, SEVIRI M-O Biases are ~ +0.5K & consistent with AVHRR In SW band (Ch4, 3.9um), the M-O biases are negative and daily means are about -2 K & inconsistent with AVHRR. During daytime, M-O biases are large and highly variable in Ch4, due to inaccurate modeling of solar reflectance. Work underway to resolve The small M-O biases in Ch4 do not mean it is accurate, as it is due to compensation of warm and cold biases in global area (see SEVIRI web).

  3. Monitoring of SEVIRI BTagainst CRTM: January 2009 In LW bands, SEVIRI M-O Biases are ~ +0.5K & consistent with AVHRR In SW band (Ch4), the M-O biases are negative and daily means are about -2 K & inconsistent with AVHRR. During daytime, M-O biases are large and highly variable in Ch4, due to inaccurate modeling of solar reflectance. Work underway to resolve

  4. SEVIRI - RTTOV From ECMWF web page Same as the case of CRTM, M-O biases in RTTOV are negative in SEVIRI IR03.9 band.

  5. SEVIRI-IASI From EUMETSAT web page The biases in Ch4 between SEVIRI and IASI are about 0.2 K and are persistent during all monitoring time.

  6. CRTM-SEVIRI (June 2008, nighttime, no solar reflectance effect) In LW bands, SEVIRI M-O Biases are not significant change compared to the whole day’s statistics. In SW band (Ch4, 3.9um), the M-O biases are about -1.5 K and the amplitude is near [-1, -2] K and are better than the whole day’s statistics [0, -4] K, which means whole day’s M-O bias largely affected by solar reflectance.

  7. CRTM-SEVIRI (January 2009, nighttime, no solar reflectance effect) In LW bands, SEVIRI M-O Biases are not significant change compared to the whole day’s statistics. In SW band (Ch4, 3.9um), the M-O biases are about -1.5 K and the amplitude are a little larger than the case of June 2008. Nighttime diurnal cycle and spikes are observed and it is due to diurnal variation in NOBS and geophysical distribution (see next slide and SEVIRI web).

  8. NOBS Frequency Significant diurnal cycle in NOBS are observed for nighttime data, and the NOBS are close to 0 near noon.

  9. Conclusion • In LW bands, SEVIRI M-O Biases are ~ +0.5K in both whole day and nighttime cases & consistent with AVHRR • In SW band (SEVIRI IR03.9), the large negative M-O biases (~-2.0 K) were observed in both the CRTM and RTTOV cases. The biases between SEVIRI and IASI are only ~+0.2 K. • In SEVIRI IR03.9 band, whole day’s statistics are largely affected by solar reflectance. • The anomaly in M-O bias is likely due to insufficient coefficient data in the RTM model for the wide IR band like IR03.9/SEVIRI. • The warm biases in some area during daytime maybe also arise from CRTM.

  10. Back-up

  11. SRF comparison between CRTM and EUMETSAT CRTM cut off spike

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