Radiometric trend of lunar calibration compared with vicarious calibration for GOSAT

Kei Shiomi1, Shuji Kawakami1, Akihiko Kuze1, Hiroshi Suto2, Taichiro Hashiguchi1, Fumie Kataoka3, Riko Higuchi4, Carol J Bruegge5, Florian Max M Schwandner5 and Lars Chapsky5, (1)JAXA, Tsukuba, Japan, (2)Japan Aerospace Exploration Agency, Tsukuba, Japan, (3)Remote Sensing Technology Center of Japan, Tsukuba, Japan, (4)RESTEC, Tsukuba, Japan, (5)Jet Propulsion Laboratory, Pasadena, CA, United States
Abstract:
GOSAT observes a nearly full moon for the on-orbit radiometric calibration of the FTS SWIR bands and the CAI. Lunar calibrations are operated in April/May for investigation of continuous annual radiometric trends and in June/July, corresponding to the annual Railroad Valley Cal/Val campaign.

JAXA’s Greenhouse Gases Observing Satellite (GOSAT) is since 2009 in polar orbit to monitor greenhouse gases such as CO2 and CH4 from space. GOSAT consists of a Fourier Transform Spectrometer (TANSO-FTS) and a Cloud and Aerosol Imager (TANSO-CAI). The FTS has 3 polarized SWIR narrow bands and a TIR wide band. The FTS observes globally with gridded points of 10 km FOV using discrete pointing. The CAI carries 4 radiometers in the UV to SWIR with high spatial resolution of 0.5-1.5 km and a wide swath of 1000 km.

Since the 3rd year, lunar calibration has been planned to observe at a phase angle around 7 degrees from normal incidence. This choice avoids the reflectance opposition surge in order to target the nearly-unchanged and brightest reflectance as a function of phase angle. The Railroad Valley vicarious calibration campaign is conducted by measuring the surface reflectance and atmospheric parameters coincident with a dedicated GOSAT target observation, to derive top-of-the-atmosphere radiance. The nadir surface reflectance is collected in 500x500 m areas corresponding to the CAI resolution. The off-nadir reflectance is measured simultaneously with BRDF values, for correction.

We will summarize the radiometric study of the GOSAT lunar calibration compared with the vicarious calibration. In-flight coincident calibration activities will continue with GOSAT and OCO-2.

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