Evaluation of Multi-Frequency SAR Images for Tropical Land Cover Mapping

Abstract

Earth Observation (EO) data plays a major role in supporting surveying compliance of several multilateral environmental treaties, such as UN-REDD+ (United Nations Reducing Emissions from Deforestation and Degradation). In this context, land cover maps of remote sensing data are the most commonly used EO products and development of adequate classification strategies is an ongoing research topic. However, the availability of meaningful multispectral data sets can be limited due to cloud cover, particularly in the tropics. In such regions, the use of SAR systems (Synthetic Aperture Radar), which are nearly independent form weather conditions, is particularly promising.With an ever-growing number of SAR satellites, as well as the increasing accessibility of SAR data, potentials for multi-frequency remote sensing are becoming numerous. In our study, we evaluate the synergistic contribution of multitemporal L-, C-, and X-band data to tropical land cover mapping. We compare classification outcomes of ALOS-2, RADARSAT-2, and TerraSAR-X datasets for a study site in the Brazilian Amazon using a wrapper approach. After preprocessing and calculation of GLCM texture (Grey Level Co-Occurence), the wrapper utilizes Random Forest classifications to estimate scene importance. Comparing the contribution of different wavelengths, ALOS-2 data perform best in terms of overall classification accuracy, while the classification of TerraSAR-X data yields higher accuracies when compared to the results achieved by RADARSAT-2. Moreover, the wrapper underlines potentials of multi-frequency classification as integration of multi-frequency images is always preferred over multi-temporal, mono-frequent composites. We conclude that, despite distinct advantages of certain sensors, for land cover classification, multi-sensoral integration is beneficial.

Above-ground biomass estimates based on active and passive microwave sensor imagery in low-biomass savanna ecosystems

“…[38][39][40] One way to make use of the sensitivity of microwaves toward different scattering mechanisms is the utilization of sensors that employ different frequencies. 41 While combinations of short and long microwaves have been successfully applied for forest biomass estimates, 42,43 only Srivastava et al 44 and Herold et al 45 confirmed their potential for thin vegetation layers. Integrating passive radar for large-scale mapping is mostly limited to soil moisture 46 or surface temperature.…”

Applications of Satellite Radar Imagery for Hazard Monitoring: Insights from Australia

“…Similar to how SAR and multi-spectral imaging provide information about different physical properties of features on the ground, SAR sensors operating at different frequencies (e.g., Table S2) provide different information due to the role of the SAR wavelength in influencing interactions of the microwave with scatterers of different sizes, the scattering mechanism (direct, double-bounce, volumetric: Section 2) and the penetration of the radar signal into the volume of ground targets. Different SAR frequency bands can be integrated for improving, e.g., LUCC classification accuracy (e.g., [24,89]), and there is currently scope to test a larger SAR frequency range than ever before with imagery now available at C-band (Sentinel-1), X-band (commercial providers), L-band (commercial providers but with future open-access from the NISAR mission due for launch in 2021, plus other missions such as ESA's ROSE-L in due course) and S-band (NovaSAR-1).…”

Spaceborne L-Band Synthetic Aperture Radar Data for Geoscientific Analyses in Coastal Land Applications: A Review

“…The Office of Space and Terrestrial Applications-1 and -3 (OSTA-1/OSTA-3) payloads flying on NASA Space Shuttle missions STS-2 and STS41G in the years 1981 and 1984 carried the experimental L-band SAR instruments Shuttle Imaging Radar-A (SIR-A) and Shuttle Imaging Radar-B (SIR-B). The Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C/X-SAR) payload was launched on the Space Shuttle Endeavour for two ten-day missions in the spring and fall of 1994 and provided the first spaceborne, multi-frequency (L-, C-X-band) SAR datasets [92][93][94].…”