Abstract
RADARSAT Constellation Mission (RCM) compact polarimetry (CP) data were simulated using 504 RADARSAT-2 quad-pol SAR images. These images were used to samples CP data in three RCM modes to build a data set with co-located ocean wind vector observations from in situ buoys on the West and East coasts of Canada. Wind speeds up to 18 m/s were included. CP and linear polarization parameters were related to the C-band model (CMOD) geophysical model functions CMOD-IFR2 and CMOD5n. These were evaluated for their wind retrieval potential in each RCM mode. The CP parameter Conformity was investigated to establish a data-quality threshold (>0.2), to ensure high-quality data for model validation. An accuracy analysis shows that the first Stokes vector (SV0) and the right-transmit vertical-receive backscatter (RV) parameters were as good as the VV backscatter with CMOD inversion. SV0 produced wind speed retrieval accuracies between 2.13 m/s and 2.22 m/s, depending on the RCM mode. The RCM Medium Resolution 50 m mode produced the best results. The Low Resolution 100 m and Low Noise modes provided similar results. The efficacy of SV0 and RV imparts confidence in the continuity of robust wind speed retrieval with RCM CP data. Three image-based case studies illustrate the potential for the application of CP parameters and RCM modes in operational wind retrieval systems. The results of this study provide guidance to direct research objectives once RCM is launched. The results also provide guidance for operational RCM data implementation in Canada’s National SAR winds system, which provides near-real-time wind speed estimates to operational marine forecasters and meteorologists within Environment and Climate Change Canada.
Highlights
Wind speed retrieval using spaceborne scatterometer and synthetic aperture radar (SAR) data is a mature field with operational implementation in many countries
Development based on European Remote Sensing (ERS-1) scatterometer data resulted in C-band model (CMOD)-IFR2 [1], with additional development producing CMOD4 and CMOD5, to arrive at CMOD5n [2] and, most recently, CMOD7 [3]
We evaluated the set of CMOD-related compact polarimetry (CP) (CMOD-CP) parameters for their utility in SAR wind speed retrieval
Summary
Wind speed retrieval using spaceborne scatterometer and synthetic aperture radar (SAR) data is a mature field with operational implementation in many countries. The most widely-used algorithms are the C-band model (CMOD) family of geophysical model functions These models were based on the relationship of the C-band vertical-transmit vertical-receive (VV) backscatter with wind speed, wind direction and incidence angle, derived from scatterometer data [1,2]. The cross-polarized backscatter, i.e., horizontal-transmit vertical-receive (HV), was associated with wind speed, without wind direction or incidence angle input [5]. Models employing both co- and cross-polarized parameters (i.e., VV and VH), in addition to incidence angle and sensor noise, with or without wind direction, were associated with wind speed and are found to be comparable to or better than CMOD-IFR2 retrievals [6]. The azimuth cutoff was explored further by [10], who establish criteria for the optimal use of azimuth cutoff for wind speed retrieval
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