Investigation of a Hybrid Algorithm for Sea Ice Drift Measurements Using Synthetic Aperture Radar Images

Areal matching by phase correlation and feature tracking are two complementary methods used to measure sea ice drift between synthetic aperture radar images. This paper evaluates a new algorithm that combines the two methods. Areal matching is improved by new methods to handle large motions and rotated ice. It is shown that areal rotation can be resolved using a frequency-domain approach. Image segmentation is a prerequisite for feature tracking and achieved by a new method that performs better than Otsu's method for two-component Gaussian mixture distributions. A circular weighted median filter is found to be suitable for the filtering of the motion field. The algorithm is evaluated through a thorough analysis of the response and sensitivity to various algorithm settings. The accuracy of the algorithm varies by up to 50% for one image pair within the studied range of parameter settings, thus indicating the need for a proper initialization of the algorithm

X-Band Interferometric SAR Observations of Baltic Fast Ice

Detailed mapping of fast-ice deformation can be used to characterize the rheological behavior of fast ice and subsequently improve sea ice modeling. This study uses interferometric synthetic aperture radar to map fast-ice deformation with unprecedented spatial resolution (meter range) and sensitivity (cm-mm range). Two interferometric acquisitions, each with a temporal baseline of 24 h, were performed by the X-band SAR satellite constellation Cosmo-SkyMed over the northeast Bay of Bothnia in the middle of the 2012 ice season. The first interferogram shows deformation of the fast ice due to force from impinging drift ice, and the normal strain within the fast ice is measured. Complementary intensity correlation measurements reveal a slow movement of the drift ice toward the fast ice. The second interferogram exhibits a low fringe rate over the fast ice with fringes being aligned along the coastline. Deformation appears to be stronger around leads, skerries, and grounded ice ridges. It is also observed that the coherence images provide information that is complementary to the information in the backscatter images

Mapping of wind-thrown forests using satellite SAR images

The study focuses on investigation and evaluation of wind- thrown forest mapping using satellite remotely sensed data from three synthetic aperture radar (SAR) sensors. The study is carried out at Remningstorp, a test site in the south of Sweden dominated by coniferous forest, where trees were manual felled to simulate wind-thrown forest. The satellite data consisted of time series of HH polarized SAR images acquired by the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR), Radarsat-2 (C-band) and TerraSAR-X (X- band). The results from visual interpretation of SAR images acquired before and after the simulated wind-throw together with corresponding ratio images show that ALOS PALSAR HH polarized intensity images are not able to detect wind- thrown forest, probably due to too coarse spatial resolution. In contrast, the wind-thrown forest is clearly visible in the Radarsat-2 and TerraSAR-X HH polarized images, implying that it may be possible to develop a new application using these SAR data for mapping of wind-thrown forests

Borealscat: A tower experiment for understanding temporal changes in P- and L-band backscattering from a Boreal forest

This paper describes the tower-based radar BorealScat, which is being developed for polarimetric, tomographic and Doppler measurements at the hemi-boreal forest test site in Remningstorp, Sweden. The facility consists of a 50-m high tower equipped with an antenna array at the top of the tower, a 20-port vector network analyser (VNA), 20 low-loss cables for interconnection, and a calibration loop with a switching network. The first version of BorealScat will perform the full set of measurements in the frequency range 0.4-1.4 GHz, i.e. P-band and L-band. The tower is currently under construction at a forest stand dominated by Norway spruce (Picea abies (L.) Karst.). The mature stand has an above-ground dry biomass of 300 tons/ha. Data collections are planned to commence in autumn 2016

BIOSAR 2010 - A SAR campaign in support to the BIOMASS mission

The ESA funded campaign BioSAR 2010 was carried out at the forestry test site Remningstorp in southern Sweden, in support to the BIOMASS satellite mission under study. Fully polarimetric SAR data were successfully acquired at L- and P-band using ONERA's multi-frequency system SETHI. In addition with other data types gathered, e.g. LiDAR and in-situ measurements, the compiled data set will be used for analyses and comparisons with biomass estimation results obtained at the same test site in the campaign BioSAR 2007, in which DLR's E-SAR made the SAR imaging. Detection of forest changes, robustness of biomass retrieval algorithms and long-term P-band coherence will be in focus as well as cross-validations between the two SAR sensors

SAR Algorithm for Sea Ice Concentration - Evaluation for the Baltic Sea

A new sea ice concentration algorithm has been developed for C-band synthetic aperture radar data. Detailed autocorrelation statistics are derived and adopted by the algorithm, and a neural network is utilized for training against 41 sea ice charts. The charts are produced by ice analysts at the Swedish Ice Service and cover the Baltic Sea. The classification of open water pixels is accurate to 94% on average, and the classification of sea ice pixels has an accuracy of 87%. This results in a root-mean-square error of 6.7 percentage points in estimating the sea ice concentration

Evaluation of a sea ice algorithm for SAR data from the Bay of Bothnia

A sea ice drift algorithm published by M. Thomas et. al. (2008) has been implemented and evaluated. Input to the algorithm is Synthetic Aperture Radar (SAR) images, which are processed using phase correlation in a multi-resolution processing system. The algorithm has been tested with horizontally co-polarized (HH) ENVISAT ASAR Wide Swath images and RADARSAT-2 ScanSAR images. The possible benefits of using cross-polarized (HV) RADARSAT-2 ScanSAR data are investigated, and initial testing of the algorithm for L-band SAR data from ALOS PALSAR has been done. The validity of the produced motion fields has been tested in three different ways. Most of the SAR images in this analysis were acquired over the Bay of Bothnia. Five meteorological stations located in this region have been collecting wind data with a temporal resolution of three hours. It is confirmed that the wind data correlates with the derived sea ice motion. Another source of validation data that has been used is the daily ice charts published by the Swedish Meteorological and Hydrological Institute (SMHI). The third method used for validation is straightforward, visual tracking of sea ice features. The algorithm is facing some difficulties when it comes to ice tracking close to the shoreline, in archipelagoes etc, since the motionless solution will be favoured. It can however be suppressed by filtering areas of land. This addition gives a more robust algorithm

Comparison between SAR derived sea ice displacement and hindcasts by the operational ocean model HIROMB

The purpose of this paper is to compare measurements of sea ice displacement from SAR imagery with ice floe drift trajectories modeled by the operational ocean circulation model HIROMB. The study examines the ice movement in the Fram Strait during a two-week period in April, 2011. The results indicate that the HIROMB model overestimates the drift speed by a factor 1 - 2.5, which may be attributed to an underestimated thickness of the ice. The model data also exhibit a directional offset in the positive clockwise direction of 10 - 30 degrees over the whole study region. The results of this study may be used to direct the model development and improve the model initialization