First Polarimetric GNSS-R Measurements from a Stratospheric Flight over Boreal Forests

Abstract

Abstract:The first-ever dual-frequency multi-constellation Global Navigation Satellite Systems Reflectometry (GNSS-R) polarimetric measurements over boreal forests and lakes from the stratosphere are presented. Data were collected during the Swedish National Space Board (SNSB)/European Space Agency (ESA) sponsored Balloon Experiments for University Students (BEXUS) 19 stratospheric balloon experiment using the P(Y) and C/A ReflectOmeter (PYCARO) instrument operated in closed-loop mode. Maps of the polarimetric ratio for L1 and L2 Global Positioning System (GPS) and GLObal Navigation Satellite System (GLONASS), and for E1 Galileo signals are derived from the float phase at 27,000 m height, and the specular points are geolocalized on the Earth's surface. Polarimetric ratio (Γ /Γ ) maps over boreal forests are shown to be in the range 2-16 dB for the different GNSS codes. This result suggests that the scattering is taking place not only over the soil, but over the different forests elements as well. Additionally to the interpretation of the experimental results a theoretical investigation of the different contributions to the total reflectivity over boreal forests is performed using a bistatic scattering model. The simulated cross-(reflected Left Hand Circular Polarization LHCP) and co-polar (reflected Right Hand Circular Polarization RHCP) reflectivities are evaluated for the soil, the canopy, and the canopy-soil interactions for three different biomass densities: 725 trees/ha, 150 trees/ha and 72 trees/ha. For elevation angles larger than the Brewster angle, it is found that the cross-polar OPEN ACCESSRemote Sens. 2015, 7 13121 signal is dominant when just single reflections over the forests are evaluated, while in the case of multiple reflections the co-polar signal becomes the largest one.

Derivation of the Cramér-Rao Bound in the GNSS-Reflectometry Context for Static, Ground-Based Receivers in Scenarios with Coherent Reflection

“…Even specific GNSS-R space-based missions have been planned by different space agencies [3,16,17]. Furthermore, more remote sensing applications have been also proposed and validated through experimental campaigns, such as: soil moisture monitoring [7,18,19,20,21,22,23,24,25], snow monitoring [26,27,28,29,30,31,32], sea-ice monitoring [33,34], ground and calm water altimetry [35,36,37,38,39,40,41,42,43] and biomass estimation [44,45]. …”

Implementation of a GNSS-R Payload Based on Software-Defined Radio for the 3CAT-2 Mission

“…It is controlled by the payload computer through an I 2 C interface to switch ON and OFF circuits and save power. The RF switching matrix is used to select between various combinations of incoming direct and reflected signals with different polarizations in order to retrieve vegetation biomass information [2].…”

“…The main objective of this nanosatellite is the demonstration of its payload PYCARO: the P(Y) and C/A ReflectOmeter. PYCARO implements a novel dual-frequency (L1 and L2) and dual-polarization (left-and right-hand circular polarizations, LHCP and RHCP) multiconstellation (GPS, GLONASS, Galileo, and BeiDou) reflectometer [2], [3] [(global navigation satellite system reflectometry (GNSS-R)] whose scientific output consists of delay-Doppler maps (DDM).…”

3Cat-2—An Experimental Nanosatellite for GNSS-R Earth Observation: Mission Concept and Analysis

“…The definitive proof of concept of payload took place in two ESA-sponsored stratospheric balloon experiments from Esrange Space Center (Sweden). The apogee was ~ 27,000 m, and PYCARO collected GNSS-R reflections mostly over boreal forests, and some lakes [24][25][26]. The 3 Cat-2 payload comprises a set of subsystems accommodated on the upper 3U volume of the structure (Figs.…”