GNSS-R payload for small satellites: design and optimization using auxiliary information

Abstract

Earth Observation (EO) using Signals of Opportunity (SoOp), the advent of high-performance and customizable Software Defined Radios (SDRs), and small satellites are revolutionizing today many Remote Sensing techniques. One of the most widely used SoOp are the Global Navigation Satellite System signals used for Radio Occultations (GNSS-RO) and Reflectometry (GNSS-R). In this last one, the reflected GNSS signals acquire properties of the surface where they are reflected, and when these signals are compared to the direct ones, one can infer surface roughness and dielectric constant information. Nowadays SDR-based GNSS-R instruments are becoming more cost-effective, power-efficient, and small enough to be adopted as CubeSats payloads. In GNSS-R receivers, all the information resides in the so-called Delay Doppler Map (DDM), which is the cross-correlation between the reflected signal and the direct one (interferometric GNSS-R or iGNSS-R), or a locally generated replica of the direct one (conventional GNSS-R or cGNSS-R) for different delays and Doppler frequency cuts. Producing these DDMs is computationally intensive due to the large number of Fast Fourier Transforms (FFTs) involved. To develop an efficient GNSS-R instrument, this work presents the development of such an instrument— the first of its kind in the United Arab Emirates (UAE)— and introduces its first operational version. Also, it explores the capture of raw GPS L1 signal, and its processing, having as auxiliary or reference information of the PRN codes of the satellites in view, and their central Doppler frequencies. The coherent and incoherent integration times will also be traded off to enhance the spatial resolution.

This research has been funded by an ASPIRE grant 24N240.

Peer Reviewed

Postprint (author's final draft)