Hotspot Signatures from Synergy of DSCOVR EPIC and Terra MISR sensors to Monitor Changes and Biophysical Processes of Equatorial Forests

In vegetation canopies, the finite size of scatters (e.g. leaves) can cast shadows. This causes a very sharp peak in retro-solar direction. This phenomenon is known as the canopy hotspot effect. The hotspot region in BRFs of vegetated surfaces represents the most information-rich directions in the directional distribution of canopy reflected radiation. The existing low-orbit sensors can measure reflectance in the hotspot region only if observations are made close to the principal plane. Such situations, however, are rare in occurrence. The NASAs Earth Polychromatic Imaging Camera (EPIC) onboard NOAAs Deep Space Climate Observatory (DSCOVR) was launched on February 11, 2015 to the Sun-Earth Lagrangian L1 point where it began to collect radiance data of the entire sunlit Earth every 65 to 110 min in June 2015. The uniqueness of the DSCOVR EPIC observing strategy is its ability to provide frequent observations of every region of the Earth in near hot spot directions that the conventional polar orbiting and geostationary satellites do not have. The DSCOVR EPIC observations therefore provide unique information required to extend limited angular sampling of the existing optical sensors to the hot spot region. Here we (i) introduce a new canopy hot spot model that synergistically incorporates features of the Terra Multi-angle Imaging SpectroRadiometer (MISR) and DSCOVR EPIC observation geometries; (ii) generate hot spot signatures of equatorial forests for the period of concurrent DSCOVR EPIC and Terra MISR data; (iii) assess their quality and (iv) demonstrate their value for monitoring changes and biophysical processes in tropical forests.