Global cloud cover for assessment of optical satellite observation opportunities: A HyspIRI case study

The number of cloud-free views by Earth-orbiting optical remote sensing instruments must be characterized to verify that the coverage is sufficient to address a mission's science objectives. This study determines the expected cloud-free coverage for the Hyperspectral Infra-red Imager (HyspIRI) mission concept using the Terra MODIS 5 km daytime cloud mask dataset covering the period 2001-2010. The HyspIRI mission concept has two instruments: a Visible Shortwave Infrared (VSWIR) imaging spectrometer and a Thermal Infrared (TIR) multispectral imager. The VSWIR and TIR instruments have equatorial revisit times of 19 and 5 days, respectively. Using the MODIS cloud mask data, we determined the percentage of the Earth's land and shallow water regions that would have been viewable with cloud-free acquisitions for each quarter and year in 2001 through 2010. For the VSWIR, the average cloud-free coverage was 83.0% quarterly and 99.6% annually. Average TIR monthly coverage was also evaluated to be 90.7%. The standard deviations for these statistics were all less than 1.2%, and the average coverages exceed HyspIRI's quarterly and annual requirements (listed in Table 6) by over twenty standard deviations. By the central limit theorem, it follows that in a typical year, HyspIRI will meet its coverage requirements (listed in Table 6) with extremely low uncertainty, acquiring a sufficient number of scenes to enable both monthly and quarterly assessments of the vast majority of the Earth's land and shallow water. This paper includes: yearly global statistics for cloud-free MODIS observations at 5 km resolution between 2001 and 2010; a one year global map representing percent cloud-free observations between 2001 and 2010; global maps representing percent cloud-free observations between 2001 and 2010 for each quarter; maps of the predicted number of views by each HyspIRI instrument quarterly and over the course of a year; and predicted global coverage quarterly and for one year for each HyspIRI instrument, with additional monthly statistics for TIR. (C) 2012 Elsevier Inc. All rights reserved.