A Simple Offset “Calibration” Method for the Accurate Geographic Registration of Ship-Borne X-Band Radar Intensity Imagery

McCann, David L.; Bell, Paul S.

doi:10.1109/access.2018.2814081

Cited by 7 publications

(9 citation statements)

References 14 publications

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“…Previous studies have successfully used data from coastal or drifting MR stations to measure sea ice motion (e.g., Karvonen, ; Rohith et al, ). To accurately retrieve sea ice drift from a ship, the MR measurements must be georeferenced, using a highly accurate position and heading sensor, and calibrated to remove offsets in the MR image heading (Lund et al, ; McCann & Bell, ). Sea ice velocity fields are derived by cross correlating pairs of temporally averaged and normalized MR sea ice images that are separated by a short (75 s) period.…”

Section: Discussionmentioning

confidence: 99%

“…For example, with R/V Sikuliaq transiting at 11 kn, a 1° bias in the MR image heading will result in a 0.1 m s −1 error in the sea ice velocity's cross‐track component. Here the ship's highly accurate Seapath compass is used, and a constant −1.32° MR image heading offset, identified following the “calibration” procedure outlined in McCann and Bell (), has been corrected for.…”

Section: Sea Ice Drift Retrieval Methodologymentioning

confidence: 99%

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Arctic Sea Ice Drift Measured by Shipboard Marine Radar

et al. 2018

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This study presents Arctic sea ice drift fields measured by shipboard marine X‐band radar (MR). The measurements are based on the maximum cross correlation between two sequential MR backscatter images separated ∼1 min in time, a method that is commonly used to estimate sea ice drift from satellite products. The advantage of MR is that images in close temporal proximity are readily available. A typical MR antenna rotation period is ∼1–2 s, whereas satellite revisit times can be on the order of days. The technique is applied to ∼4 weeks of measurements taken from R/V Sikuliaq in the Beaufort Sea in the fall of 2015. The resulting sea ice velocity fields have ∼500 m and up to ∼5 min resolution, covering a maximum range of ∼4 km. The MR velocity fields are validated using the GPS‐tracked motion of Surface Wave Instrument Float with Tracking (SWIFT) drifters, wave buoys, and R/V Sikuliaq during ice stations. The comparison between MR and reference sea ice drift measurements yields root‐mean‐square errors from 0.8 to 5.6 cm s−1. The MR sea ice velocity fields near the ice edge reveal strong horizontal gradients and peak speeds > 1 m s−1. The observed submesoscale sea ice drift processes include an eddy with ∼6 km diameter and vorticities <–2 (normalized by the Coriolis frequency) as well as converging and diverging flow with normalized divergences <–2 and >1, respectively. The sea ice drift speed correlates only weakly with the wind speed (r2 = 0.34), which presents a challenge to conventional wisdom.

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Section: Discussionmentioning

confidence: 99%

Section: Sea Ice Drift Retrieval Methodologymentioning

confidence: 99%

Arctic Sea Ice Drift Measured by Shipboard Marine Radar

et al. 2018

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“…Furthermore, care must be given to identify and remove offsets in the radar image orientation. Here, this is accomplished using the ''calibration'' method detailed in McCann and Bell (2018).…”

Section: Methodsmentioning

confidence: 99%

Near-Surface Current Mapping by Shipboard Marine X-Band Radar: A Validation

Lund

Haus

Horstmann

et al. 2018

Journal of Atmospheric and Oceanic Technology

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The Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters to measure submesoscale upper-ocean currents and their potential impact on oil spills. The experiment was conducted from January to February 2016 in the Gulf of Mexico (GoM) near the mouth of the Mississippi River, an area characterized by strong submesoscale currents. A Helmholtz-Zentrum Geesthacht (HZG) marine X-band radar (MR) on board the R/V F. G. Walton Smith was used to locate fronts and eddies by their sea surface roughness signatures. The MR data were further processed to yield near-surface current maps at ~500-m resolution up to a maximum range of ~3 km. This study employs the drifter measurements to perform the first comprehensive validation of MR near-surface current maps. For a total of 4130 MR–drifter pairs, the root-mean-square error for the current speed is 4 cm and that for the current direction is 12°. The MR samples currents at a greater effective depth than the CARTHE drifters (1–5 m vs ~0.4 m). The mean MR–drifter differences are consistent with a wave- and wind-driven vertical current profile that weakens with increasing depth and rotates clockwise from the wind direction (by 0.7% of the wind speed and 15°). The technique presented here has great potential in observational oceanography, as it allows research vessels to map the horizontal flow structure, complementing the vertical profiles measured by ADCP.

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“…For the same reason, it is crucial that any shipboard MR installation be calibrated to identify and correct for offsets in the relative angle between ship and radar heading. Here, this is accomplished following the calibration method introduced by McCann and Bell (). The method uses image processing techniques to determine the calibration parameters that maximize the contrast of fixed MR targets, which must be observed from different viewpoints.…”

Section: Methodsmentioning

confidence: 99%

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

et al. 2020

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This study evaluates shipboard marine X‐band radar (MR) near‐surface current and bathymetry measurements under shallow water conditions. The retrieval algorithm is based on the surface wave signal within three‐dimensional wave number frequency MR backscatter intensity variance spectra. The MR data were collected during a research cruise that investigated submesoscale processes and their impact on oil spill transport in the Louisiana Bight. The MR currents and bathymetry are validated using measurements from 500 GPS‐equipped surface drifters, a shipboard acoustic Doppler current profiler, and a shipboard single‐beam echo sounder. Earlier results from the same experiment but using a different set of sensors indicate strong upper ocean vertical current shear over a 3.5 hr period, despite only mild wind forcing. Here, the MR currents are derived as a function of wave number, providing a measure of vertical shear for the full duration of the cruise. Strong vertical shear is frequently observed, with a maximum difference of 0.42 m/s between the MR high (effective depth of ∼0.9 m) and low ( ∼2.4 m) wave number bins. Treating the drifter and echo sounder measurements as truth, the accuracies of the MR near‐surface currents and bathymetry are 0.04–0.07 m/s and 1.2 m (or 7% of the mean water depth). However, it is shown that ∼50% of the MR high wave number and drifter current differences is due to vertical shear. The shallow water MR near‐surface current accuracy thus matches findings from a previous deep water validation where vertical shear was much weaker.

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A Simple Offset “Calibration” Method for the Accurate Geographic Registration of Ship-Borne X-Band Radar Intensity Imagery

Cited by 7 publications

References 14 publications

Arctic Sea Ice Drift Measured by Shipboard Marine Radar

Arctic Sea Ice Drift Measured by Shipboard Marine Radar

Near-Surface Current Mapping by Shipboard Marine X-Band Radar: A Validation

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

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