The Spatial-sampling Charcteristics of Global Optical Imagers: Implications on Product Interconsistency over Land And Coastal Waters

Abstract:

With the increasing need to construct long-term climate-quality data records to understand, monitor, and predict climate variability and change, it is vital to continue systematic satellite measurements along with the development of new technology for more quantitative and accurate observations. The Suomi-NPP mission provides continuity in monitoring the Earth’s surface and its atmosphere in a similar fashion as the heritage MODIS instruments onboard NASA’s Terra and Aqua satellites. The reflective properties of the Earth surface, including land surface reflectance (LSR) and remote sensing reflectance (R_rs) in costal waters, are among the essential climate variables from which higher-level products relevant to biological and biogeochemical activities can be explored. In this study, we aim at quantifying consistency amongst Aqua-MODIS, Terra-MODS, and the Suomi-NPP VIIRS LSRs as well as R_rs in coastal waters (Level-2). To avoid interferences from sources of measurement and/or processing errors other than spatial sampling, including calibration, atmospheric correction, and the effects of the Bidirectional Reflectance Distribution Function (BRDF), the MODIS and VIIRS Level-2 products are simulated using the Landsat-8’s Operational Land Imager (OLI) Level-2 products. The simulations are performed using the instruments’ point spread functions on a daily basis for various OLI scenes over a 16-day revisit cycle. Preliminary results over land targets show that the daily mean biases (computed over the entire OLI area) in LSRs due to spatial sampling remain below 0.0015 (1%) in absolute surface reflectance. Overall, the disparity increases when VIIRS viewing zenith angle is larger than that of MODIS. Similar trends were observed for the simulated NDVI products. Depending on the spatial heterogeneity of the OLI scenes, per-grid-cell differences can reach up to . Further spatial analysis of the NDVI and LSR products revealed that depending on the user requirements for product intercomparisons different spatial scales might be used. It was found that if per-grid-cell differences on the order of 10% (in LSR or NDVI) are tolerated, the product intercomparisons are expected to be immune from effects of spatial sampling. The analysis over coastal waters is currently ongoing.