The Performance and Potentials of the CryoSat-2 SAR and SARIn Modes for Lake Level Estimation

Karina Nielsen,Per Knudsen,Ole Andersen,Lars Stenseng

doi:10.3390/w9060374

Abstract

Over the last few decades, satellite altimetry has proven to be valuable for monitoring lake levels. With the new generation of altimetry missions, CryoSat-2 and Sentinel-3, which operate in Synthetic Aperture Radar (SAR) and SAR Interferometric (SARIn) modes, the footprint size is reduced to approximately 300 m in the along-track direction. Here, the performance of these new modes is investigated in terms of uncertainty of the estimated water level from CryoSat-2 data and the agreement with in situ data. The data quality is compared to conventional low resolution mode (LRM) altimetry products from Envisat, and the performance as a function of the lake area is tested. Based on a sample of 145 lakes with areas ranging from a few to several thousand km 2 , the CryoSat-2 results show an overall superior performance. For lakes with an area below 100 km 2 , the uncertainty of the lake levels is only half of that of the Envisat results. Generally, the CryoSat-2 lake levels also show a better agreement with the in situ data. The lower uncertainty of the CryoSat-2 results entails a more detailed description of water level variations.

Highlights

Satellite altimetry has played an increasingly important role in lake level estimation over the past 20 years, where the number of gauges has been declining
We have predicted CryoSat-2 and Envisat water levels for 145 lakes to evaluate the performance of the Synthetic Aperture Radar (SAR) and SAR Interferometric (SARIn) modes compared to conventional altimetry
Based on the results found in this study, it can be concluded that the CryoSat-2 derived lake levels have a significant lower median of standard deviation (MSD) compared to Envisat for lakes with an area smaller than 1000 km2

Summary

Introduction

Satellite altimetry has played an increasingly important role in lake level estimation over the past 20 years, where the number of gauges has been declining. The TOPEX/Poseidon and the Jason 1–3 satellites were/are operating in a 10-day repeat cycle, while the European Remote Sensing (ERS) 1 and 2, Envisat, and Saral/Altika satellites were operating in a 35-day repeat cycle. Many of these conventional missions, with a footprint diameter of several kilometers, were originally intended for ocean applications. Some of the first results were obtained by [1], who estimated water level time series of lakes and reservoirs with the TOPEX/Poseidon satellite, and thereby demonstrating a successful use of satellite altimetry for hydrology applications. [6] validated water levels obtained from the different retrackers available from Envisat over the Amazon basin with in situ data, and Ref. Ref. [6] validated water levels obtained from the different retrackers available from Envisat over the Amazon basin with in situ data, and Ref. [7] demonstrated that reliable water level estimates can be obtained from Envisat over narrow branches of the Mekong River by accounting for the hooking

Methods

Discussion

Conclusion