A revisit to the GNSS-R code range precision

TL;DR

This paper critically reviews existing models for GNSS-R code range precision, proposes an improved CRB-based approach, and finds that actual performance may be significantly worse than previous estimates, affecting oceanography and tsunami detection applications.

Contribution

It introduces a CRB-based model for better estimation of reflected signal range precision in GNSS-R, improving upon previous assumptions.

Findings

CRB-based predictions are four times worse than previous models.

The impact on oceanography and tsunami detection is significant.

Provides closed-form expressions for signal analysis.

Abstract

We address the feasibility of a GNSS-R code-altimetry space mission and more specifically a dominant term of its error budget: the reflected-signal range precision. This is the RMS error on the reflected-signal delay, as estimated by waveform retracking. So far, the approach proposed by [Lowe et al., 2002] has been the state of the art to theoretically evaluate this precision, although known to rely on strong assumptions (e.g., no speckle noise). In this paper, we perform a critical review of this model and propose an improvement based on the Cramer-Rao Bound (CRB) approach. We derive closed-form expressions for both the direct and reflected signals. The performance predicted by CRB analysis is about four times worse for typical space mission scenarios. The impact of this result is discussed in the context of two classes of GNSS-R applications: mesoscale oceanography and tsunami detection.