Survey of Hyperspectral Earth Observation Applications from Space in the Sentinel-2 Context
be (R.d.A.); email@example.com (A.M.); firstname.lastname@example.org (P.D.) Abstract: In the last few decades, researchers have developed a plethora of hyperspectral Earth Observation (EO) remote sensing techniques, analysis and applications. While hyperspectral exploratory sensors are demonstrating their potential, Sentinel-2 multispectral satellite remote sensing is now providing free, open, global and systematic high resolution visible and infrared imagery at a short revisit time.
... recent launch suggests potential synergies between multi-and hyper-spectral data. This study, therefore, reviews 20 years of research and applications in satellite hyperspectral remote sensing through the analysis of Earth observation hyperspectral sensors' publications that cover the Sentinel-2 spectrum range: Hyperion, TianGong-1, PRISMA, HISUI, EnMAP, Shalom, HyspIRI and HypXIM. More specifically, this study (i) brings face to face past and future hyperspectral sensors' applications with Sentinel-2's and (ii) analyzes the applications' requirements in terms of spatial and temporal resolutions. Eight main application topics were analyzed including vegetation, agriculture, soil, geology, urban, land use, water resources and disaster. Medium spatial resolution, long revisit time and low signal-to-noise ratio in the short-wave infrared of some hyperspectral sensors were highlighted as major limitations for some applications compared to the Sentinel-2 system. However, these constraints mainly concerned past hyperspectral sensors, while they will probably be overcome by forthcoming instruments. Therefore, this study is putting forward the compatibility of hyperspectral sensors and Sentinel-2 systems for resolution enhancement techniques in order to increase the panel of hyperspectral uses. (MIVIS), etc., hyperspectral research quickly expanded the number of hyperspectral applications in vegetation monitoring, water resources management, geology and land cover     . However, they do not allow regular and synoptic coverages over large areas as spaceborne sensors. Moreover, spaceborne sensors produce images with lower angular effects due to their much smaller field of view. Despite the technological advances, hyperspectral satellites are still poorly represented in the spaceborne missions compared to multispectral ones, even considering forthcoming launches. Two hyperspectral missions for EO started around 2000 and were decisive in the progress of hyperspectral application development and demonstration. Hyperion (EO-1 platform) was first launched in 2000 and recorded data with a 30-m GSD and 400-2500 nm as the spectral range ( Figure 1 ). Compact High Resolution Imaging Spectrometer (CHRIS) is fully programmable (i.e., in spatial resolution, total swath and spectral band settings) and provides five distinct angular views  . However, since this sensor does not cover the SWIR range, CHRIS was excluded from this hyperspectral application review. Several hyperspectral missions will shortly be launched, such as the PRISMA (PRecursore IperSpettrale della Missione Applicativa) Italian mission with a 30-m GSD and a wavelength range of 400-2505 nm  , the EnMAP (Environmental Mapping and Analysis Program of 30-m GSD, 420-2500 nm) German mission  and the HISUI (Hyperspectral Imager SUIte of 30-m GSD, 400-2500) Japanese mission  . This low number of hyperspectral spaceborne instruments is mainly due to technical and practical constraints including challenging Signal-to-Noise Ratio (SNR) in particular bottom-of-atmosphere reflectance, sensor cost, data volume and associated data processing cost and time  . Several studies demonstrated the potential of hyperspectral sensors in a wide range of applications from geology  , to vegetation [16, 17] , water resources [10,18] and land cover  . Each of these reviews focused on a very limited number of application subjects, missing a more comprehensive overview of hyperspectral remote sensing findings.