Abstract 2023: Marco Casu - The Geological Remote Sensing Group (GRSG)

GRSG 34th Conference 2023

Title: Sale’e Porcus Spectral library V1.0

Author: Marco Casu

Within the context of emerging orbiting hyperspectral sensors like ASI-PRISMA and EnMAP DLR, as well as upcoming continuity missions (ASI-PRISMA SG, ESA CHIME), there is an escalating demand from user communities for ground reflectance spectra, essential for the reliance on remotely sensed data. From this perspective, during June and July 2023, three field operations were conducted to gather surface spectroscopy data in Sale’e Porcus site (SPp), located in
western Sardinia (Italy), a salty pond primarly composed of consistent salts that dries up completely during the summer season. This plain and almost homogeneous reflective surface is an ideal natural location for CAL/VAL purposes (Calibration and Validation).

The campaigns were carried out taking in account both ASI-PRISMA and EnMAP DLR 30-meter spatial resolution and a spectral resolution of approximately 10 nm in the VNIR-SWIR wavelength range. To match these specifications a Malvern Panalytical FieldSpec 3 Pro portable spectroradiometer operating in the same spectral range was used to gather data and start the construction of a dedicated spectral library. The data collection process involved both field and laboratory activities. The field activities encompass spectra collection, based on two distinct acquisition schemes: a Random Acquisition Geometry (RAG), in order to maximize the impact of spatial variation of the outcropping evaporites on the statistical analysis of the collected surface reflectance, and a Geometrically Defined Geometry (GDG), in order to collect points considering that PRISMA and EnMAP satellites have an inclination on the equator passage of about 8.5° and a minimum pixel size of 30x30m.

The fiber optic was aligned towards the target at an angular inclination opposite to the solar incidence angle. Subsequently, Spectra were adjusted to absolute reflectance using a Spectralon white reference panel. Physical samples during the second campaign were collected following identical acquisition geometries and later analyzed in the laboratory through an X;Pert Pro PANalytical X-Ray Diffractometer (XRD) for investigating their crystallographic structure and detecting their mineralogical composition. This work presents initial phases of the release of the SPp spectral library, containing samples representing a limited range of materials that exhibit slight variations across different temporal and spatial domains. Presently, the library includes 403 visible shortwave infrared (VNIR/SWIR) spectra alongside 15 mineralogical samples.

The mineralogical analyses have highlighted the predominance of essential minerals characteristic of the evaporite series, notably including calcite, dolomite, ankerite, gypsum, and halite. Here the outcomes of preliminary activities dedicated to building a specialized spectral library for the Sal’e e Porcus pond are described. This research unveils the results of initial efforts dedicated to building a specialized spectral library for the Sal’e e Porcus pond.This is planned for ongoing expansion and updates, aiming to enhance its usefulness as ground truth for aerial and spaceborne hyperspectral sensors such as PRISMA and EnMAP.

Within the context of emerging orbiting hyperspectral sensors like ASI-PRISMA and EnMAP DLR, as well as upcoming continuity missions (ASI-PRISMA SG, ESA CHIME), there is an escalating demand from user communities for ground reflectance spectra, essential for the reliance on remotely sensed data. From this perspective, during June and July 2023, three field operations were conducted to gather surface spectroscopy data in "Sale’e Porcus'' site (SPp), located in western Sardinia (Italy), a salty pond primarly composed of consistent salts that dries up completely during the summer season. This plain and almost homogeneous reflective surface is an ideal natural location for CAL/VAL purposes (Calibration and Validation). The campaigns
were carried out taking in account both ASI-PRISMA and EnMAP DLR 30-meter spatial resolution and a spectral resolution of approximately 10 nm in the VNIR-SWIR wavelength range.

To match these specifications a Malvern Panalytical FieldSpec 3 Pro portable spectroradiometer operating in the same spectral range was used to gather data and start the construction of a dedicated spectral library. The data collection process involved both field and laboratory activities. The field activities encompass spectra collection, based on two distinct acquisition schemes: a Random Acquisition Geometry (RAG), in order to maximize the impact of spatial variation of the outcropping evaporites on the statistical analysis of the collected surface reflectance, and a Geometrically Defined Geometry (GDG), in order to collect points considering that PRISMA and EnMAP satellites have an inclination on the equator passage of about 8.5° and a minimum pixel size of 30x30m. The fiber optic was aligned towards the target at an angular inclination opposite to the solar incidence angle.

Subsequently, Spectra were adjusted to absolute reflectance using a Spectralon white reference panel. Physical samples during the second campaign were collected following identical acquisition geometries and later analyzed in the laboratory through an X'Pert Pro PANalytical X-Ray Diffractometer (XRD) for investigating their crystallographic structure and detecting their mineralogical composition. This work presents initial phases of the release of the SPp spectral library, containing samples representing a limited range of materials that exhibit slight variations across different temporal and spatial domains. Presently, the library includes 403 visible shortwave infrared (VNIR/SWIR) spectra alongside 15 mineralogical samples.