Gu Songyan, Wu Ronghua, You Ran. The analysis and correction of lunar intrusion to space view of FY-3A/MWHS. J Appl Meteor Sci, 2015, 26(4): 442-450. DOI:  10.11898/1001-7313.20150406.
Citation: Gu Songyan, Wu Ronghua, You Ran. The analysis and correction of lunar intrusion to space view of FY-3A/MWHS. J Appl Meteor Sci, 2015, 26(4): 442-450. DOI:  10.11898/1001-7313.20150406.

The Analysis and Correction of Lunar Intrusion to Space View of FY-3A/MWHS

DOI: 10.11898/1001-7313.20150406
  • Received Date: 2014-12-30
  • Rev Recd Date: 2015-03-31
  • Publish Date: 2015-07-31
  • The microwave humidity sounder (MWHS) is an important payload of FY-3A launched on 27 May 2008, for global all-weather atmosphere sounding. FY-3A/MWHS has been in operational application on orbit for more than 5 years. FY-3A/MWHS has five channels in the range of 150-191 GHz. In the normal working mode, it performs a cross-track scanning and cycle two points calibration by using of the blackbody and space views. However, the moon may occasionally appear within the cold space calibration field of view. Due to the polar orbit of the platform, it will always appear to be near the-90 phase and then have a brightness temperature of approximately 170-200 K. Its angular extent is about 0.5. Lunar radiation could therefore be significant against a cold sky background, especially for the narrow-beamed MWHS. Lunar intrusion to space view of MWHS may make a moon-glint, which typically affects about 100 scan lines per orbit for 4-5 consecutive orbits. Lunar intrusion cases are detectable as the degradation in NWP model statistics.Based on analysis of lunar intrusion cases and effects, a mitigation algorithm is developed to improve calibration results of FY-3A/MWHS in orbit.In the algorithm, the position of the moon is calculated using standard astronomical formula, and the intruding time is flagged. After that an approximation by polynomial model is devised to remove the moon-glint. On 4 July 2010, the moon-glint makes more than 1000 digital number abnormal jumping, and 20 degree degradation in brightness at sub-points line for FY-3A/MWHS 183.31±1 GHz channel.By using of the cross calibration technique between corresponding channels of FY-3/MWHS and MetOp-A/MHS, an extensive analysis is carried out to make the best fitted global SNO samples.The lunar intrusion mitigation algorithm is tested, and results show that after removing the moon-glint effects, corrected calibration results are almost the same with what got during check in orbit. The lunar intrusion mitigation algorithm works well and has been used in operation, providing the foundation of quantitative application for data of FY-3A/MWHS in NWP. Lunar intrusion also gives a clear view of the moon when it appears in the field of space view. Since there is no intervening atmosphere to attenuate the signal, which makes it possible to perform a cross-channel calibration.
  • Fig. 1  Impact on space view from moon-glint

    (a) space view, (b) black body view, (c) space view contaminated by moon-glint, (d) black body view matching with Fig. 1c

    Fig. 2  The change of space view data between scan-lines during a moon-glint

    Fig. 3  The basic data distribution during an orbit observation

    Fig. 4  The distribution of space view data for FY-3A/MWHS 183.31±1 GHz channel over orbits on 22 Jul 2008

    Fig. 5  Sketch map of FY-3/MWHS affected by the moon

    (a) Scanning sketch map of FY-3/MWHS when the moon in space area,(b) moon solid angle to FY-3 satellite center

    Fig. 6  Sketch map of how the moon affecting on the FY-3A/MWHS space view

    Fig. 7  Brightness temperature for sub-points during an orbit observation

    (a) brightness temperatures for sub-point lines,(b) earth views for sub-point lines,(c) space views

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    • Received : 2014-12-30
    • Accepted : 2015-03-31
    • Published : 2015-07-31


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