[A-CG39] 北極域の科学

[ACG39-P11] 複数の衛星搭載光学センサデータから抽出された北半球積雪域分布の比較

*堀 雅裕¹、庭野 匡思^2,3、青木 輝夫^3,2、島田 利元⁴ (1.富山大学都市デザイン学部、2.気象庁気象研究所、3.極地研究所、4.宇宙航空研究開発機構地球観測研究センター)

キーワード：積雪域、衛星光学センサ、リモートセンシング 、気候、北半球

Snow cover extent (SCE) is a key variable to be observed from space for assessing the impacts of global warming on the Earth’s climate. SCE in the Northern Hemisphere has been monitored using various satellite sensors during the past 40 years and several SCE datasets are currently available (e.g., Estilow et al., 2015, Hori et al., 2017). However, long-term trends of SCE derived from the SCE datasets are not consistent partly because the input data from which SCEs are determined are different among the datasets and also because the detection criteria of snow cover for a dataset has been changed during the observation period (which was inevitable due to the operational purpose in a meteorological agency as seen in the case of the NOAA CDR dataset). In order to derive a credible long-term trend in SCE, in this study, we compare the SCEs derived from several optical sensors (MODIS onboard Terra satellite, MODIS onboard Aqua satellite, VIIRS onboard SUOMI-NPP satellite) using the same method (Hori et al., 2017) and examine the consistency and the causes for the differences among the SCEs. Preliminary analysis revealed that the SCE from SUOMI-NPP/VIIRS is consistent well with that from Aqua/MODIS (R²=0.9992) with slight negative biases of about a few percent in snowy season. When comparing SCEs derived from MODISs on both Terra and Aqua satellites with VIIRS/SCE, the consistency become slightly lower (R²=0.9982) and the biases become larger up to around 7-8%. The possible causes of the biases are the followings; 1) differences in the observation time (i.e., Terra observes the Earth in the morning, whereas SUOMI-NPP and Aqua observes in the afternoon), 2) differences in the instantaneous field of view (IFOV) of the sensor (MODIS is 1km, whereas VIIRS is 750m). To explore the causes for the differences in SCEs derived from the three satellite sensors further, spatial differences of the SCE maps are compared and the results will be discussed.

Reference:
Estilow, T.W., A.H. Young and D.A. Robinson, 2015: A long-term northern hemisphere snow cover extent data record for climate studies and monitoring. Earth Syst. Sci. Data, 7, 137–142.
Hori, M. et al., 2017: A 38-year (1978-2015) Northern Hemisphere daily snow cover extent product derived using consistent objective criteria from satellite-borne optical sensors. Remote Sens. Environ., 191, 402-418.