The hyperspectral sensors DESIS for aquatic ecosystems monitoring - a sensitivity study

Abstract

The aquatic ecosystems of coastal and inland waters are more variable than the open ocean as water constituents and bottom substrates differ considerably in type, concentration and optical properties. Sensors with high spatial, spectral and radiometric resolution are therefore required to provide enough detail for mapping these highly complex environments. Two new hyperspectral Earth observation instruments, designed for monitoring spectrally complex areas, are the DLR Earth Sensing Imaging Spectrometer (DESIS) and the Environmental Mapping and Analysis Program (EnMAP). These hyperspectral sensors both cover a spectral range from 420 nm to 1000 nm in VNIR (and 900 nm -2450 nm in SWIR for EnMAP) and have a spatial resolution of 30 meters. DESIS was already launched to the ISS in summer 2018, EnMAP’s launch date will be in 2020. The goal of the present study is to specifically evaluate the performance of DESIS and EnMAP over aquatic ecosystems based on their sensor specifications. For this purpose, a sensitivity study was conducted in order to explore the spectral and radiometric properties of DESIS and EnMAP in the context of optically deep and shallow water mapping. The optical water properties and benthic cover types were chosen to represent typical inland and coastal waters. Forward simulations of hyperspectral measurements were made using the Water Color Simulator software WASI to study the expected DESIS and EnMAP radiances and their signal-to-noise ratios (SNR) for different atmospheric conditions. The impact of sensor noise on the retrieval of water constituents, benthos types and water depth was analyzed by applying inverse modelling to these reflectance spectra. The study assesses the mapping potential and limitations of a DESIS and EnMAP type sensor for these complex environments, which are usually much darker than land surfaces.