Simulating Multi-Directional Narrowband Reflectance of the Earth’s Surface Using ADAM (A Surface Reflectance Database for ESA’s Earth Observation Missions)

Abstract

The ADAM (A Surface Reflectance Database for ESA’s Earth Observation Missions) product (a climatological database coupled to its companion calculation toolkit) enables users to simulate realistic hyperspectral and directional global Earth surface reflectances (i.e., top-of-canopy/bottom-of-atmosphere) over the 240–4000 nm spectral range (at 1-nm resolution) and in any illumination/observation geometry, at 0.1° × 0.1° spatial resolution for a typical year. ADAM aims to support the preparation of optical Earth observation missions as well as the design of operational processing chains for the retrieval of atmospheric parameters by characterizing the expected surface reflectance, accounting for its anisotropy. Firstly, we describe (1) the methods used in the development of the gridded monthly ADAM climatologies (over land surfaces: monthly means of normalized reflectances derived from MODIS observations in seven spectral bands for the year 2005; over oceans: monthly means over the 1999–2009 period of chlorophyll content from SeaWiFS and of wind speed from SeaWinds), and (2) the underlying modeling approaches of ADAM toolkit to simulate the spectro-directional variations of the reflectance depending on the assigned surface type. Secondly, we evaluate ADAM simulation performances over land surfaces. A comparison against POLDER multi-spectral/multi-directional measurements for year 2008 shows reliable simulation results with root mean square differences below 0.027 and R2 values above 0.9 for most of the 14 land cover IGBP classes investigated, with no significant bias identified. Only for the “Snow and ice” class is the performance lower pointing to a limitation of climatological data to represent actual snow properties. An evaluation of the modeled reflectance in the specific backscatter direction against CALIPSO data reveals that ADAM tends to overestimate (underestimate) the so-called “hot-spot” by a factor of about 1.5 (1.5 to 2) for barren (vegetated) surfaces.

Comment on “Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum” by K. Michaelian and A. Simeonov (2015)

“…3. In many other cases algae cause a decrease in reflectance at short wavelengths, and an increase above about 500 nm, both for phytoplankton (Jin et al, 2002(Jin et al, , 2011Bacour et al, 2020;Li et al, 2021) (Fig. 5) and for brown and green macroalgae (Qi and Hu, 2021).…”

“…The data in Fig. 4 do not extend over a sufficiently wide wavelength range to permit such a comparison, but we show the calculation for Bacour et al (2020) and Jin et al (2002) in Fig. 5.…”

“…5. Based on the data of both Bacour et al (2020) and those of Jin et al (2002), more light is reflected from water containing more algae. This holds on an energy basis, and the increase in reflected light by the algae is even more pronounced when expressed on a photon basis.…”

“…Ultraviolet radiation has played an important role in the prebiotic synthesis of the molecular species that have made the origin of life possible (Björn, 2015). But several recent publications explore the possibility that the first life emerged in places without any ultraviolet radiation or visible light, such as submarine hydrothermal vents (Altair et al, 2021) or a geyser system driven by nuclear power (Maruyama et al, 2019).…”

Performance Estimation of a Medium-Resolution Earth Observation Sensor Using Nanosatellite Replica

“…The observed objects will be assumed to be Lambertian surfaces, reflecting light like ideal diffusers. This is a common assumption in the field of Earth Observation, including the visible and SWIR regions [10,[34][35][36], although it is true that the reflectance properties of an object can be better described using more complex models [6,[36][37][38].…”