Presentation Information
[AAS08-P23]Evaluation of cloud coverage estimation within GOSAT-2/TANSO-FTS-2 FOV by the GOSAT-2 onboard RGB camera
*Masashi Hirose1, Naoko Saitoh1 (1.Center for Environmental Remote Sensing, Chiba University)
Keywords:
GOSAT-2,Intelligent Pointing System,Himawari-8/AHI,Cloud judgement
In the data processing of GOSAT-2/TANSO-FTS-2, cloud contamination within the observation field of view (FOV) is evaluated for each observation and retrieval of greenhouse gas concentrations is carried out only when the FOV is judged as clear-sky. GOSAT-2 has been newly equipped with "Intelligent Pointing System (IPS)" that uses a visible camera to monitor the FOV of TANSO-FTS-2 for avoiding cloudy scenes. In this study, we evaluated whether the IPS identifies clouds within the TANSO-FTS-2 FOVs as expected, using reflectance and brightness temperature data of Himawari-8/AHI.
First, we extracted coincident observations of Himawari-8/AHI and TANSO-FTS-2 over the ocean for each season (January, April, July, and October) of 2020. Using the extracted Himawari-8/AHI data, we conducted several tests for detecting clouds within the TANSO-FTS-2 FOVs and calculated the fraction of cloud coverage within the FOV. Here, we followed the methods of MODIS cloud judgements [Ackerman et al., 1998; MODIS MOD35 ATBD, 2010] and determined the thresholds of the cloud tests based on Saitoh and Kitamura [2021]. We then calculated "H8−IP", defined as the difference between the cloud fraction based on Himawari-8/AHI cloud judgement and the cloud fraction of the IPS.
Overall, the ratio of better agreement of cloud fractions between Himawari-8 and IPS (H8−IP within ±0.1) was highest in January (37.8%) and lowest in July (29.8%), and the ratio of the observation scenes where the IPS largely missed clouds (H8−IP larger than 0.7) was highest in October (28.1%) and lowest in April (19.7%). Observation scenes where the Himawari-8’s cloud fraction was larger than the IPS’s cloud fraction were dominant in all the latitude bands from 60°N to 60°S. Especially during the winter of mid-to-high latitude bands in both hemispheres, the IPS had a tendency to miss clouds. During the summer in both hemispheres, in contrast, the ratio of better agreement of cloud fractions between Himawari-8 and IPS (within ±0.1) was higher, indicating that the IPS did not miss clouds at most scenes in the mid-high latitude summer.
Detailed evaluation based on the category classification of the Himawari-8/AHI cloud judgement tests ("low-level clouds," "high-level thick clouds," and "high-level thin clouds") showed that the IPS could detect low-level thick clouds with high accuracy, while it is likely to miss high-level thin clouds such as cirrus clouds. Clouds missed by the IPS in the mid-high latitude winter, in particular, were likely to be high-level clouds detected by the cloud judgement tests of thermal infrared bands of Himawari-8/AHI. For the future work, it should be checked whether clouds that the IPS missed due to its characteristics of the RGB camera were surely detected by subsequent cloud judgements by TANSO-CAI-2 and TANSO-FTS-2 SWIR band.
First, we extracted coincident observations of Himawari-8/AHI and TANSO-FTS-2 over the ocean for each season (January, April, July, and October) of 2020. Using the extracted Himawari-8/AHI data, we conducted several tests for detecting clouds within the TANSO-FTS-2 FOVs and calculated the fraction of cloud coverage within the FOV. Here, we followed the methods of MODIS cloud judgements [Ackerman et al., 1998; MODIS MOD35 ATBD, 2010] and determined the thresholds of the cloud tests based on Saitoh and Kitamura [2021]. We then calculated "H8−IP", defined as the difference between the cloud fraction based on Himawari-8/AHI cloud judgement and the cloud fraction of the IPS.
Overall, the ratio of better agreement of cloud fractions between Himawari-8 and IPS (H8−IP within ±0.1) was highest in January (37.8%) and lowest in July (29.8%), and the ratio of the observation scenes where the IPS largely missed clouds (H8−IP larger than 0.7) was highest in October (28.1%) and lowest in April (19.7%). Observation scenes where the Himawari-8’s cloud fraction was larger than the IPS’s cloud fraction were dominant in all the latitude bands from 60°N to 60°S. Especially during the winter of mid-to-high latitude bands in both hemispheres, the IPS had a tendency to miss clouds. During the summer in both hemispheres, in contrast, the ratio of better agreement of cloud fractions between Himawari-8 and IPS (within ±0.1) was higher, indicating that the IPS did not miss clouds at most scenes in the mid-high latitude summer.
Detailed evaluation based on the category classification of the Himawari-8/AHI cloud judgement tests ("low-level clouds," "high-level thick clouds," and "high-level thin clouds") showed that the IPS could detect low-level thick clouds with high accuracy, while it is likely to miss high-level thin clouds such as cirrus clouds. Clouds missed by the IPS in the mid-high latitude winter, in particular, were likely to be high-level clouds detected by the cloud judgement tests of thermal infrared bands of Himawari-8/AHI. For the future work, it should be checked whether clouds that the IPS missed due to its characteristics of the RGB camera were surely detected by subsequent cloud judgements by TANSO-CAI-2 and TANSO-FTS-2 SWIR band.