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 5km 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 5days, 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 5km 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.