Abstract
This is the second part of a study on how temporal sampling frequency affects satellite retrievals in support of the Deep Space Climate Observatory (DSCOVR) mission. Continuing from Part 1, which looked at Earth’s radiation budget, this paper presents the effect of sampling frequency on DSCOVR-derived cloud fraction. The output from NASA’s Goddard Earth Observing System version 5 (GEOS-5) Nature Run is used as the “truth”. The effect of temporal resolution on potential DSCOVR observations is assessed by subsampling the full Nature Run data. A set of metrics, including uncertainty and absolute error in the subsampled time series, correlation between the original and the subsamples, and Fourier analysis have been used for this study. Results show that, for a given sampling frequency, the uncertainties in the annual mean cloud fraction of the sunlit half of the Earth are larger over land than over ocean. Analysis of correlation coefficients between the subsamples and the original time series demonstrates that even though sampling at certain longer time intervals may not increase the uncertainty in the mean, the subsampled time series is further and further away from the “truth” as the sampling interval becomes larger and larger. Fourier analysis shows that the simulated DSCOVR cloud fraction has underlying periodical features at certain time intervals, such as 8, 12, and 24 h. If the data is subsampled at these frequencies, the uncertainties in the mean cloud fraction are higher. These results provide helpful insights for the DSCOVR temporal sampling strategy.
Highlights
Orbiting around the Sun–Earth L1 Lagrange point, the two instruments on board the Deep SpaceClimate Observatory (DSCOVR) spacecraft, the Earth Polychromatic Imaging Camera (EPIC) and the National Institute of Standards and Technology Advanced Radiometer (NISTAR), provide observations on the entire sunlit side of the Earth continuously [1]
Deep Space Climate Observatory (DSCOVR)-like observations have been assessed using a range of different metrics in Part 1 of this study ([4]—hereafter, Part-1)
The cloud fraction is output from the Nature Run every half hour, which is adopted as the “truth”
Summary
DSCOVR can only discretely sample the Earth’s climate system. Factors such as the dowlink bandwidth and receiver antenna availability affect the number of observations that can be sent back. As has been shown in previous studies, this subsampling will affect the accuracy of satellite retrieved parameters [2,3]. The potential effects of temporal sampling frequency on the Earth’s radiation budget derived from. DSCOVR-like observations have been assessed using a range of different metrics in Part 1 of this study ([4]—hereafter, Part-1). Another important product of DSCOVR-EPIC is the cloud fraction
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