GSICS activities and strategy plan in CMA CMA GPRC, 2012

Outline FY-2 GSICS GEO-LEO IR calibration monitoring Long term bias analysis Operational Implementation Experiences from GSICS FY-3 inter-calibration CRCS Sites and global sites calibration Inter-calibration with MODIS and GOME-2 DCC Unified calibration strategy of FY sensors

FY-2 IR Calibration Milestones Before 2005: Earlier FY-2A/2B IR calibration based on Vicarious Calibration using Qinghai Lake and had no real time or near real time operational cal. Early sensor worked instably and has heavy stray light and didn’t have good geolocation. After 2005: FY-2C can work stably and VISSR IR operational calibration based on inter-calibration using AVHRR and HIRS since 2005. FY-2D/2E also continues this kind of operational model since they begun to work operationally. After 2009: FY-2C/2D GSICS IR calibration experiment using the AIRS and IASI since Oct., 2009. Development of onboard half-optical BB calibration model based on GSICS reference standard. After 2011: FY-2D/2E operational calibration monitoring test using GSICS IR calibration since May, 2011. FY-2E GSICS GEO-LEO IASI results has become the operational input of L1 calibration LUT instead of AVHRR/HIRS since Jan 12, 2012. After 2012: FY-2F/2G/2H completely operational calibration based on GSICS calibration using AIRS/IASI or CrIS and diurnally adjustment using half-optical BB calibration model. Retrospectively: Recalibration for FY-2C/2D/2E is conducted based inter-calibration using AIRS and IASI.

FY-2D/2E Calibration Trend

FY-2C/2D calibration bias

FY-2E calibration bias Old operational Cal GSICS Cal

FY-2D Double Difference Tb in four Times

FY-2E Double Difference Tb in four Times

Stray light on the FY-2 calibration

FY-2 GSICS operation Implementation We think that it is the best way if GSICS calibration result directly generates NEW LUT which is the same as the L1 format. This way for data user is very convenient and not needed to update the L2 code package. The specific Implementation of GSICS Correction for FY-2: The independent LUT txt file on every day for history data. Add the GSICS new LUT SDS into the L1 HDF file (Named: CALChannelIR1…) Follow the GSICS Correction criterion in NetCDF output at the same time FY-2E GSICS GEO-LEO IASI results has become the operational input of L1 calibration LUT instead of AVHRR/HIRS since Jan 12, 2012. And the update frequency is one or two weeks considering different phases of FY-2. FY-2D operational calibration will also base on GSICS calibration using IASI in nearly future after testing. FY-2F directly operational calibration based on GSICS calibration using IASI or CrIS and diurnally adjustment using half-optical BB calibration model.

GSICS Findings in FY-2 GSICS monitoring shows that the calibration of FY-2 IR bands has clear bias whose fluctuation is large and more than 1.1 K (bias deviation for long term) using inter-calibration evaluation with AIRS and IASI. Water vapor IR3 has the largest bias and deviation in FY-2C/2D/2E with more than -2 K bias and the deviation of 1.5 K, which are caused by little quality control and using the incorrect spectral adjustment in the operational calibration with HIRS. The Double difference Temperature (DDT) of FY-2 imagers with independent AIRS and IASI performs excellent consistence for the 290 K reference scene and is about 0.2K uncertainty in stable phase for long period. The difference in the four times of inter-calibrations with the AIRS and IASI in each day is used to evaluate the diurnal feature of FY-2 calibration. There is a large fluctuation of DDT in spring and autumn eclipse phase and the largest diurnal change appears for all the IR bands at 21:30 PM. The water vapor channel always has great diurnal change at 1:30AM. The stray light effects on calibration can be seen for the cold 220k targets in FY-2C/2D using the DDT technique. This leads to great calibration uncertainty in random oscillation at different time. FY-2E’s DDT is relatively stable compared with FY-2C/2D for clod targets with small deviation and verifies the instrument improvement of FY-2E in the stray light restriction. There are many valuable lessons from the GSICS inter-calibration system, which provides a good chance to improve and correct the operation calibration accuracy of FY-2 satellites.

Experiences from GSICS GSICS is monitoring the FY-2 VISSR instruments calibration trend on orbit and indicates the annual and season fluctuation of operation calibration bias. GSICS gives FY-2 VISSR a good independent radiance reference standard and enhances FY-2X calibration tying to international SI. GSICS results verify the improvement of instrument manufacture step by step and provide positive feedback to the vendor. GSICS also provides a tie bridge of consistent calibration between geostationary FY-2 IR and polar orbiting FY-3 IR bands using the same GSICS advised sensors.

Latest FY-2F GSICS Calibration using IASI

FY-3B/IRAS Inter-Cal with IASI IRAS and IASI collocated samples of Jan~ Jun, 2011 were used. Ground distance is less than 10 km . Time difference is less than 10 minutes. 5×5 IASI pixels and 3×3 IRAS pixels were chosen to comparing, inhomogeneous observations .

Comparison of convolved IRAS radiance and operational FY3B/IRAS observations for mapped samples

Positive bias

Positive bias

Error[K] Channel Number

FY-3/MERSI spectral bands FY-1A/1B MVISR-1 FY-1C/1D MVISR-2 FY-3A/3B/3C VIRR MERSI-1 FY-3D/3E/3F FY-3/MERSI-II 1 0.58-0.68 0.63 0.470 2 0.725-1.1 0.865 0.550 3 3.75 0.650 4 10.8 5 10.5-12.5 12.0 11.25 1.24/1.03 6 1.61 1.640 1.64 7 0.455 2.130 2.13 8 0.48-0.53 0.49 0.412 9 0.53-0.58 0.55 0.443 10 0.94 1.36 0.490 11 0.520 0.555 12 0.565 0.670 13 0.709 14 0.685 0.746 15 0.765 16 0.905 17 0.936 18 0.940 19 0.980 1.38 20 1.030 3.8 21 4.050 22 7.2 23 8.550 24 25

China Radiometric Cal Sites (CRCS) Dunhuang site and Qinghai Lake Surface reflectance measurement ASD field spectroradiometer CE313 field radiometers (simulated MERSI and VIRR’s bands) Atmospheric characteristics measurement Weather and radiosonde Sunphotometer: AOD, transmittance OL754 spherical integrating sphere spectroradiometer Calibration method: Reflectance-based method Irradiance-based method Radiance-based method by glider The glider Hu X.Q, J. Liu, L.Sun, Z. Rong, Y. Li, Y. Zhang, “Characterization of CRCS Dunhuang Test Site and Vicarious Calibration Utilization for Fengyun(FY) Series Sensors, ” Can. J. Remote Sensing, Vol. 36, No. 5, pp. 566–582, 2010

Multi-sites calibration with global stable targets : Gobi and desert targets: Dunhuang, Libya1, Libya4 and Arabia2, ocean site: Lanai (MOBY). Multi-sites with different brightness to cover more position in dynamic range of the sensor ; Multi-sites and multi-days to provide more opportunities and decrease the random error. Dunhuang (40.138°N, 94.32°E) Libya1 (24.42°N, 13.35°E) MERSI can not realize the onboard absolute radiometric calibration in the solar bands. The annual vicarious calibration based on synchronous in-situ measurements at Dunhuang has been the main calibration method for MERSI. But the data amount is limited not enough for frequent in-flight calibration coefficient updates. To increase the calibration frequency, we choose 5 sites with stable surface properties, including Libya4 (28.55°N, 23.39°E) Arab2 (20.13°N, 50.96°E) Lanai (20.49°N, -157.11°E)

Calibration Coefficient Trending (0.470, 50) Calibration Coefficient Trending (0.550, 50) Blue dot for CRCS VC (0.650, 50) (0.865, 50)

Normalized Change Trending

FY-3A MERSI Response Change based global sites calibration Onboard Calibration (VOC) To Dec. 31, 2011

FY-3B MERSI Response Change To Dec. 31, 2011

Inter-Calibration with MODIS Liu J.J, Z. LI, Y. L. Qiao, Y.-J. Liu, Y. X. Zhang, “A new method for cross -calibration of two satellite sensors, ” Int. J. Remote Sensing, 10 December, 2004, VOL. 25, NO. 23, 5267–5281, 2004.

Iner-Cal between MERSI and GOME-2 Band Cal_Slope Reflectance Uncertainty Spatial Total 1 0.0002669 0.16 0.72 0.74 2 0.0002677 0.15 0.89 0.91 3 0.0002508 0.14 0.98 0.99 8 0.0002384 0.18 0.68 0.70 9 0.0002232 0.23 0.69 0.73 10 0.0002065 0.21 0.78 0.81 11 0.0002102 0.86 0.88 12 0.0002016 0.93 13 0.0002063 1.03 1.05 14 0.0001806 1.06 1.09 15 0.0001871 1.14 1.16

Blue Channels Using DCC

Red Channels(1) Using DCC

Red Channels(2) Using DCC

Near infrared Channels Using DCC

Degradation during 2008-2010 All the Cal methods show the same degradation trend and have a good consistence except of the water absorption bands 17, 18,19. The band 18 appears significant difference of degradation from different methods.

Unified Calibration Strategy for FY Sensors

The End