Simulating Reality by Assessing Mast Impact at the Gobabeb GHNA Calibration Site
The Gobabeb site is located next to the Gobabeb Research and Training Centre in Namibia. This desert research station lies in the Namib Desert at the confluence of three distinct ecosystems: the Namib Sand Sea, the gravel plains, and the Kuiseb River. The site hosts several instruments to characterise the surface reflectance and atmospheric properties. It is part of several networks such as AERONET, HYPERNETS Namibia (GHNA) or a radiometric calibration site (GONA) as part of the RadCalNet network (Bialek et al., 2016)
Ground observations acquired at the GHNA site play a critical role in the validation and calibration of geophysical products derived from satellite observations. As such, these measurements are expected to serve as highly accurate reference data. However, the measurements themselves can be influenced by the way they are performed and by elements present in the surrounding environment.
DTE-S2GOS offers the unique capability to simulate both ground- and space-based observations within realistic 3D environments. In this study, the GHNA mast supporting the Hypstar®-XR radiometer was incorporated into the Gobabeb 3D scene. This allowed us to investigate how the presence of the mast may influence the acquisition of surface reflectance, also referred to as the Hemispherical–Conical Reflectance Factor (HCRF).
To assess this effect, HCRF was simulated both with and without the mast. The simulation performed without the mast—where the Hypstar-XR® instrument was effectively suspended in the air—was considered the ideal reference case. The comparison shows that, depending on the viewing geometry, the presence of the mast can affect the magnitude of the observed reflectance by more than 1%.
These results highlight the potential of DTE-S2GOS to realistically reproduce observation conditions and to quantify how elements of the measurement setup may influence the recorded signal.
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