FY-3C/MERSI characterization evaluation based on CMA GISCS platform on early orbit Xiuqing(Scott) Hu, Na Xu, Ronghua Wu, Ling Sun, Lin Chen, Hanlie Xu, Ling Wang National Satellite Meteorological Center, CMA
Outline Background MERSI instrument Performance evaluation Calibration assessment Conclusion
Background FY-3C launched on 23 September 2013 with the third Medium Resolution Imaging Spectrometer (MERSI). FY-3C initiated the operational running era of China’s second generation of polar- orbiting meteorological satellites FY-3 serials after two experimental satellites FY-3A and FY-3B. MERSI was turned on September 30, 2013 and open its solar reflective bands and then it’s IR bands started to work on October 17, FY-3C/MERSI has some remarkable improvements with respect to the MERSI onboard on FY-3A and FY-3B. SNR Improvement in these bands 1~4 (250m spatial resolution) Enhance the consistency of the spectral response function (SRF) in different detectors within one band, especially for the thermal Infrared band (band 5). Extended the field of viewing for space view (SV) for the lunar calibration. Radiometric response stability of solar bands is better than FY-3A and FY-3B which have great degradation in short wavelength bands ( <500nm).
FY-3A Launched on 5/27/08 local equator-crossing time: 10:30 AM (descending southward) First light on 6/4/08 FY-3B Launched on 11/05/10 local equator-crossing time: 1:30 PM (ascending northward) First light on 11/12/20 Background FengYun-3: Near-sun-synchronous polar orbit Nominal altitude: 836 km Data website :
20 spectral bands with a total of 350 detectors located on 4 focal plane assemblies (FPA). –19 reflective solar bands (RSB): bands 1- 19, 0.4~2.1um –1 thermal emissive bands (TEB): band 5, um Two spatial resolutions (nadir): 250 m(1- 5), and 1 km(6-20) Scan angle: ±55° (from nadir) –A swath of 10 km (along-track) by 2900 km (nadir along-scan) –Global coverage in 1 day One-sided 45 scan mirror with one K- mirror (de-rotation) –1.5 second each scan A broad range of applications –Near 20 science data products for studies of the Earth’s land, ocean, and atmosphere properties. Medium Resolution Spectral Imager (MERSI) Made by Shanghai Institute of Technology and Physics (SITP), Chinese Academy of Sciences (CAS) (Hu, X, IEEE, 2012)(Hu, X, IEEE, 2012)
MERSI continuity and Evolution Futural MERSI-2 Five more IR bands Circurrus Clould Band 1.38um Has two IR split windows with 250m spatial resolution Cover all bands in VIRR and MERSI-1 Higher accuracy from onboard calibration Has Lunar Calibration Band FY-1A/B MVISR-1 FY-1C/D MVISR-2 FY-3A/B/C VIRR FY-3A/B/C MERSI-1 FY-3D/E/F MERSI-II
FY-3C MERSI Event log on orbit DateEvent LogDescription Open and get first imageSuccessfully image collection Take off the cooler baffleFor IR band working Turn on VOC （ AB,A,B) Check the initial response change ~11 Turn on VOC （ AB,A,B) Monitor the degradation Open IR band (b5 ） IR image is good and has weak stripping First SV moon observationGet moon disk for lunar calibration ~27 Turn on VOC （ AB,A,B) Monitor the degradation Close the onboard normalized processing Downlink the raw image data and the stripping is heavier （ 5,6,7,8,18,20) ~07 Turn on VOC （ AB,A,B) Monitor the degradation Update the new normalized LUT in DPPS L1 Image stripping is better ~21 Turn on VOC （ AB,A,B) Monitor the degradation SV moon observationGet moon disk for lunar calibration ~16 Turn on VOC （ AB,A,B) Monitor the degradation SV moon observationGet moon disk for lunar calibration ~12 Turn on VOC （ AB,A,B) Monitor the degradation
FY-3A MERSI’s de-rotation K mirror stop working and its SWIR bands 6 and 7 are influenced by anomalous electronic gain jumps, possibly induced by electrostatic discharge. For FY-3B MERSI, the baffle of radiative cooler was not successfully opened. Thus, bands 5, 6 and 7 are operated in anomalous working conditions without temperature control since Jan. 21, 2011, and band 5 is inoperable. FY-3C MERSI is working perfectly by now.
Performance evaluation In-orbit verification (IOV) of the instrument performance specification of FY-3C/MERSI started to be conducted in middle October, Some representative performances were derived, including signal noise ratio (SNR), dynamic range saturation restore function. modulation transfer function (MTF), band-to band registration, calibration accuracy consistency of the multiple detector, instrument stability
FY-3C/MERSI SRF: Better consistency of multi-detector in Infrared band 3A_IR5 3C_IR5 MERSI spectral response function (SRF) of each detectors of band 5 in FY-3A (left) and FY-3C(right)
SNR: SNR: Noise equivalent reflectance (NE ) or Noise equivalent temperature (NEdT) ,7 8,9 10~16 17~20 Red ： Specification Blue ： Preflight Green ： inflight Noise equivalent reflectance (NE ) or Noise equivalent temperature (NEdT) of each detector of FY-3A MERSI solar reflective bands on-orbit calculated using the space view data during the commissioning phase. The at the solar bands (Bands 1–4 and 6-20) was largely beyond the specifications except for some detectors at band 6 and 7 as shown in above Figure.
MERSI SNR Comparison in FY-3A/B/C BandWavelengthSpecification3A SNR3B SNR3C SNR3C inflight K Great SNR improvement
Saturation Restore
MTF (along track)
MTF (along scanning)
De-overlap processing MERSI has 27% overlap along scanning Image is better after de-overlap processing m MERSI before and after de-overlap in two scenes
MTF after de-overlap
Calibration verification and evaluation Onboard calibration Visible onboard calibrator , Space view lunar calibration Inter-calibration SNO: IASI CrIS /MODIS /GOME-2 /VIIRS Cross calibration using PICS Itself Inter-comparison within FY-3A/3B/3C Comparison between different sensor with same bands Test Site calibration Multi-sites 、 CRCS （ Summer, 2014 ） Global Stable sites monitoring Desert 、 snow 、 DCC 、 sunglint
FY-3/MERSI VOC Solar cone Two Internal lamps Mini interaged sphere 扩束准直系统 Trap detector monitoring
VOC monitoring First onboard visible calibration prototype device for FY series. The VOC’s output is a parallel light source from the beam expanding system. Although the radiance can’t be calculated exactly, it is relatively stable and monitored by trap detectors. When lamps are turned on or the sun enters the light cone, it can be used to monitor the temporal radiometric response changes. (Hu, X, IEEE, 2012)(Hu, X, IEEE, 2012)
VOC solar signal normalization
Lunar calibration for MERSI Moon images in FY-3C/MERS’s space viewing for four times on December 20, 2013
SV lunar Observe FY3B :05 FY3C :15 FY3C :05 250m SV image 1km SV image
First result of Lunar calibration Ban d WL/nmPreflight : : : :
Inter-calibration for FY-3C/MERSI The cross-calibration became the most important approach for the evaluation of FY-3C/MERSI calibration accuracy. We conducted the calibration evaluation for the solar bands using LEO-LEO SNO data from EOS/MODIS, NPP/VIIRS and Metop- A/GOME-2. It was found that the difference from different calibration methods and need further analysis to provide the calibration coefficient update based on the integration of these methods. GSICS LEO-LEO IR method was used to MERSI band 5 based on Metop/IASI and NPP/CrIS. Figure 3 shows the bias of MERSI IR band is keeping within 0.5K with respect to CrIS.
GSICS Public Platform (Hu, X, IEEE, 2013)(Hu, X, IEEE, 2013)
FY-3C/MERSI-METOP-A/IASI FY-3C/VIRR-METOP-A/IASI Mean Bias 0.57±0.29K Mean Bias CH4 ： -1.01±0.47K CH5 ： -0.95±0.38K FY-3C/MERSI/VIRR IR using IASI (Xu, N, Remote Sensing, 2014)(Xu, N, Remote Sensing, 2014)
FY3C/MERSI has good consistency with NPP/CrIS Bias is less than 0.5 K and higher than CrIS Bias has no large temperature dependence FY-3C/MERSI using CrIS
MERSI IR Bias Trend: stable Calibration bias trend and standard deviation of MERSI band 5 using NPP/CrIS during December, 2013 based on the CMA GSICS platform
Xcal using MODIS
MERSI with Terra/MODIS
MERSI with GOME-2
MERSI using Metop-A/GOME-2
MERSI comparison with NPP/VIIRS band Wl (um) width (nm) VIIRS M M I1/M I2/M I5/M M M M M M M M M M M M8
Dunhuang (40.138°N, 94.32°E)Libya1 (24.42°N, 13.35°E) Libya4 (28.55°N, 23.39°E)Arab2 (20.13°N, 50.96°E) Lanai (20.49°N, °E) Gobi and desert targets: Dunhuang, Libya1, Libya4 and Arabia2; ocean site: Lanai (MOBY). Multisite calibration tracking TOA radiation calculation similar as CRCS VC, but without in-situ measurements.
Multi-site Cal (Sun, L, IEEE, 2012)(Sun, L, IEEE, 2012)
Degradation rate based on Multi-sites Cal Bandk1k0 2 σ /Mean(%) Annual DegradationRate(%) 12.45E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E
Cal results using several methods Cal Method PreflightLunar Multi-sites Xcal using MODIS date2013/12/212013/10/52013/12/152013/12/202013/12/232013/12/ E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-02 We are finding the reason of this kind of large difference from the results of different methods. Maybe the large no-linearity lead to the different results because they worked in different dynamic range in different method.
Instrument Stability monitoring The instrument performance monitoring (IPM) system for FY- 3C/MERSI is also being developed using the telemetry and engineering data of the instrument Radiometric stability is monitored by the earth viewing data of global PICS (deserts, salt lakes, snow and DCC). The current most information show the relatively stable status of the instrument operational running and there is no obvious degradation of FY-3C MERSI instrument radiometric response. The long term stability monitoring using 4 deserts of Pseudo Invariant Calibration Sites (PICS) during the first three months from Oct. to Dec, The results indicate that FY- 3C/MERSI is more stable than the previous instruments.
MERSI Instrument Performance Monitoring using OBC files ParameterDescription DimensionUsage MERSI_imageryMERSI Quick View imagery of the global Earth ViewRGB(3,2,1)Check EV data integrity and quality Earth Invariant TargetsInvariant targets EV data of all MERSI bands, DCC 20 bands, 4 GeoAngles and LatLon Ev monitoring using Desert, snow Telemetry temperatures BB, RTA, cavity, HAM, FPA, cooler, Mainframe, Circuit Card Assembly 21 tempsInstrument Healthy status Health and Status TelemetryMotor current, DC store current, Instrument operation status VOC_Counts MERSI observation DN of Solar diffuser for band I1~I3, M1~M11, DNB over band average 19 bandsDegradation trending VOC NEdDNNoise NEdN for VOC signal of solar bands19 bandsSNR trending VOC_Counts by detectors MERSI observation DN of Solar diffuser I1~I3, M1~M11, DNB over detector average 19bands *40(10)detdegradation for Detector uniform VOCSM signalVOCSM signal of VOC and Sun in every orbit8 bandsVOC trending SV_CountsMERSI observation Space view DN for 20 bands20bandsBackground signal trending SV NEdDNDark Noise NEdN for Space view signal20bandsDark noise signal BB_CountsMERSI observation Blackbody DN for 20 bands20 bandsIR gain derivation BB NEdDNNoise NEdN for black body signal20bandsIR bands noise F factors and H factors Degradation of Solar bands based on VOC signal and VOCSM, solar incident angles to VOC and VOCSM 19 bandsSolar bands degradation SNRSignal to noise ratio for 19 solar bands19 VIS bandssolar bands noise NEDT Noise equivalent temperature for 7 IR bands I4, I5, M12-M16 IR bandsIR bands noise IR Calibration GainCalibration gains for IR bands M4, M5, M12-M16 IR bandsIR calibration trending Lunar CalibrationLunar observation data collection and Analysis19 bandsSolar bands degradation
Instrument status is stable
Global Stable Site monitoring Libya1 Libya4 Arabia2 Algeria3 Algeria5Sonora Uyuni_salt
TOA reflectance trend: No apparent degradation FY-3C/MERSI Long term stability monitoring using 4 deserts of PICS during the first three months from Oct. to Dec, 2013
Conclusion FY-3C/MERSI overcame the several problems existed in FY-3A and FY-3B and is better than the previous. It has significant improvement in some performances as following ： Better SNR Better consistency of the SRF in different detectors within IR band Provide the possibility SV lunar calibration. Better Radiometric response stability of solar bands ( <500nm). These good performances are important for its long term operation and quantitative application.
The End Thanks for your attention