21-EPN-FT1-025: Ammonium salts reflectance spectra changing viewing geometry for distinguish them on the surface of icy planetary bodies
Visit by Maximiliano Fastelli and Matteo Bisolfati, University of Perugia (Italy), to TA2.8 CSS (Cold Surfaces Spectroscopy) at IPAG (France).
Dates of visit: 13-25 June 2022
Report Summary: During the Europlanet 2024 RI TA Fast Track call, reflectance VIS-NIR spectra were collected at the CSS facility (IPAG) in Grenoble, France. Different viewing geometries were chosen to collect BRDF spectral data of a selected group of ammonium minerals. BRDF were collected in the 1 – 4.8 μm range considering a set of 3 incidence angles (i) (i = 0°; 30°; 60°) and 8 emergence angles (e) between -70° and 70° at room temperature. The NH4+overtone and combination bands located at ~ 1.09, 1.32, 1.62, 2.04, 2.2 and 3.05 μm are experimentally investigated.
The bands position remains unchanged varying geometrical configuration. On the other hand bands area and depth shows the highest values for i = 0° and 30° and e below 40°. These band parameters at ± 70° emergence angles evidence a decrease in their values. A general trend of spectral red shift with phase angle is observed. The bidirectional reflectance spectroscopy of selected samples shows important variations with the observation geometry of the measurements. Furthermore, from these preliminary data analyses, can be observed how reflectance values and spectral slope are affected by geometry of measurements. The surfaces of the planetary bodies are irregular and rough, which is why the effect of the observation geometry must also be considered. The collected data set can be helpful in the context of future missions aimed to understand the nature of minerals on icy and small bodies. NH4+–bearing minerals identification has a strong impact on understand their thermal evolution and the construction of geophysical internal models.
