Abstract
In this paper, we present the Software PARIS Interferometric Receiver (SPIR), a high-speed GNSS reflectometry recording receiver which has been designed and implemented with the primary goal of demonstrating the synoptic capabilities of the interferometric technique in GNSS Reflectrometry. Thanks to the use of large bandwidth GNSS signals, this technique is advantageous in comparison to the so-called clean-replica processing, when sea surface altimetric applications are pursued. The SPIR receiver down-converts, samples, and records the GNSS signals acquired by the sixteen elements of two antenna arrays. It can operate at any of the common GNSS L1, L2, or L5 bands. Digital beam-forming and signal processing is performed off-line by its dedicated signal processor, so that the GNSS reflectometry can be applied to different transmitting satellites using the same set of recorded signals. Alternatively, different processing techniques can be compared by applying them to exactly the same signals. This article focuses on the SPIR instrument hardware and software, as well as the remote sensing observables that can be obtained using this equipment.
Highlights
Introduction and State of the ArtGNSS (Global Navigation Satellite System) signals reflected from the surface of the sea can be used to infer its physical properties, such as the sea-surface roughness [1] and altimetry [2].This measurement concept is known as GNSS Reflectometry (GNSS-R) or as PAssive Reflectometry and Interferometry System (PARIS)
The DE4 board is populated with a Stratix IV Field Programmable Gate Array (FPGA) and its function is to interface with the Software PARIS Interferometric Receiver (SPIR) front-end to control and program the different subsystems, in addition to gathering the 16 digital data-streams to be recorded on the computer
This section describes the two main post-processing steps applied to the SPIR raw data set to obtain waveforms, which are the main observables in GNSS-R: a beamformer and a correlator
Summary
GNSS (Global Navigation Satellite System) signals reflected from the surface of the sea can be used to infer its physical properties, such as the sea-surface roughness [1] and altimetry [2]. To demonstrate synoptic altimetric measurements with the iGNSS-R technique, we have developed the Software PARIS Interferometric Receiver (SPIR) This instrument collects raw data from all individual elements of two antenna arrays of eight elements at a high rate (320 MBytes/s) and saves them to solid state disks, and all data samples are recorded with precise time-tagging with respect to UTC (Coordinated Universal Time) time. This paper first describes the instrument hardware and its software processor It shows instrument validation measurements for significant subsystems and presents a selection of observables (waveforms) using the clean-replica and interferometric techniques which were acquired during an airborne campaign over the Baltic Sea. The paper ends with some concluding remarks
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