AHI IR Tb bias variation diurnal & at low temperature Arata Okuyama and Masaya Takahashi Meteorological Satellite Center, Japan Meteorological Agency 2017 GRWG/GDWG Annual Meeting, 20-24 March 2017, Madison, USA

1. Diurnal variation analysis of AHI-8 and AHI-9 as an ideal case of GEO-GEO approach, SBAF ~= 1.0, so to say, full-time ray-matching

Diurnal variation in IR Tb Tb Biases at the std.radiance Himawari-8/AHI [K] [K] MTSAT-2/Imager [K] [K] AHI-8 doesn’t have significant diurnal variation seen in MTSAT-2, but small variation still exists. [K] [K] [K] [K] [K] [K] [K] [K] [K] Reference sensors: Metop-A/IASI Metop-B/IASI Aqua/AIRS S-NPP/CrIS [K] midnight Dec. 2014 [UTC] [UTC] [UTC] Dec. 2015 3

AHI-8 and AHI-9 Tb bias at the std. scene Diurnal variation of Tb bias for AHI-9 is as small as AHI-8. Hyper-sounder based approach is effective to know diurnal variation, but “gap” exists. Himawari-8/AHI 　　　　 Himawari-9/AHI Tb biases [K] Tb biases [K] [UTC] [UTC] 14 -28 Feb 2017 14 -28 Feb 2017

GEO-GEO approach by AHI-8/9 B08 (6.2 um) AHI-9 EW gradation? AHI9 – AHI8 stray light AHI-9 Tb matches that of AHI-8 very well. GEO-GEO approach can be of help to know spatial pattern of the Tb bias. [K] [K] AHI-8 [K] AHI-9 [K] AHI9 – AHI8 [K] Averaged Tb in 19x19 pix grid is plotted. Data region is SSP +/- 30 deg.

GEO-GEO approach by AHI-8/9 GEO-LEOs (AHI-9) GEO-GEO (AHI9–AHI8) 0.0K -0.5K +0.5K Band 8 (6.2 um) Tb biases [K] 0.0K -0.5K +0.5K Band 9 (6.9 um) 0.0K -0.5K +0.5K Band 10 (7.3 um) 14 – 19 Feb 2017. Vertical lines show 00 UTC. [UTC] Global averaged Tb difference at the standard temp. The Tb diff. is corrected based on SRF difference. 14 -28 Feb 2017

GEO-GEO approach by AHI-8/9 AHI-9 has Tb bias jump, around 0.1 K, twice per day. Not so many GEO-LEO collocation data in a timing of the jumps GEO-GEO approach is effective in such case. GEO-GEO approach: is available in 24 hrs. can reveal diurnal variation in finer temporal resolution. can illustrate spatial distribution of bias. is relative comparison, which can’t utilize state-of-the-art LEO instruments. Best way would be a blending of GEO-LEO + GEO-GEO approaches, but, how to decide the biases and its uncertainty at each time of a day?

2. AHI-8 Tb bias for lower temperature Response to: Action GIR.2016.3o.1: Arata to check how the cold end corrections are behaving using AIRS.

From my presentation in the last annual meeting... Bias in “cold end” Uncertainty of brightness temperature (Tb) bias tends is larger in lower Tb range, especially in SWIR. Some meteorologists are interested in cold region. It is caused by non-linearity between radiance and Tb and is significant in shorter wavelength. Is such the large bias true? Tb bias is -5 K at 220 K, -15 K at 210K. The corrected radiance become minus in Tb < 207 K. Planck’s law says... [W･m-2･sr-1･(μm)-1] 3.9 um 6.2 um 10.4 um 300 K 0.6021 5.682 9.823 200 K 0.00128 0.1187 0.9703 Energy is 1/470

AHI-8 Tb bias stability for lower temperature Tb bias is stable. Estimated Tb bias deviation is larger for lower temperature. Time series of Tb biases between the hyper sounders and Himawari-8/AHI Band 12 (9.6μm) w.r.t. S-NPP/CrIS 　　 w.r.t. Aqua/AIRS 　　 w.r.t. Metop-A/IASI at 290K at 290K at 290K +1.5 +1.5 +1.5 -1.5 -1.5 -1.5 2015 2016 2015 2016 2015 2016 at 250K at 250K at 250K +1.5 +1.5 +1.5 -1.5 -1.5 -1.5 2015 2016 2015 2016 2015 2016 at 220K at 220K at 220K +1.5 +1.5 +1.5 -1.5 -1.5 -1.5 2015 2016 2015 2016 2015 2016 Stable AHI Tb biases w.r.t. CrIS at cold scenes Daily 29 days statistics for GSICS correction

Standard error of Tb bias The standard error based on AIRS and CrIS tend to be smaller in Band 7, 8, and 11, even though there are wide gap-channels around the bands. Standard error of Tb bias at 220 K B07 (3.9 um) B08 (6.2 um) B09 (6.9 um) B10 (7.3 um) B11 (8.6 um) B12 (9.6 um) B13 (10.4 um) B14 (11.2 um) B15 (12.4 um) B16 (13.3 um) Reference sensors: Metop-A/IASI Metop-B/IASI Aqua/AIRS S-NPP/CrIS

Band 11 Band 8 Band 7

Summary GEO-GEO comparison: Tb bias for lower temperature: The approach is available in 24 hrs, can reveal diurnal variation in finer temporal resolution. can illustrate spatial distribution of the Tb bias, and is relative comparison, which can’t utilize state-of-the-art LEO instruments. Best way would be a blending of GEO-LEO + GEO-GEO approaches, but, how to decide the biases and its uncertainty at each time of a day? Tb bias for lower temperature: Likun commented that the IASI on-board processing is not performing well enough in the cold end and noted that AIRS do not have that particular problem. (c.f. minutes of the last annual meeting) Confirmed. Action GIR.2016.3o.1  close

Tb bias Tb bias shows large variation for Band 7, 8, and 11 w.r.t. AIRS and CrIS because of wide gap-channels around the bands. Tb bias at 220 K Reference sensors: Metop-A/IASI Metop-B/IASI Aqua/AIRS S-NPP/CrIS

Standard error of Tb bias at 250 K

Standard error of Tb bias at 290 K

AHI data quality (Tb bias vs location) What is an uneven plot in the diurnal variation? Collocation data location depends on time of day and equatorial crossing time of LEO satellite. Assuming that GEO Tb bias depends on observed location, the uneven plot might be appeared at the timing of reference sensor change. Further investigation is required. AHI Band 12 (9.6um) vs. IASI-A # of collocation data Mean TB bias TB bias in each longitudinal bin ~clear scene 2 x 2 degrees grid statistics for 2015 (Sep. - Nov.)

B08 AHI9 – AHI8 AHI8 AHI9