Abstract
Moored upward-looking Acoustic Doppler Current Profilers (ADCPs) can be used to observe sea ice draft. While previous studies relied on the availability of auxiliary pressure sensors to measure the instrument depth of the ADCP, we present an adaptive approach that infers instrument depth from ADCP bottom track (BT) mode measurements of error velocity and range. The ADCP-derived ice draft time series are validated with data from adjacent Upward-Looking Sonar (ULS) moorings. We demonstrate that this method can be used to obtain daily mean sea ice draft time series that, on average, are within 20% of ULS-derived draft time series. ULS and ADCP ice draft time series were observed by four moorings in the Laptev Sea and show correlations between 0.7 and 0.9. This new approach is not a substitute for high-frequency, high-precision ULS measurements of ice draft but it provides a low-cost opportunity to derive daily mean ice draft time series accessing existing ADCP data that have not been not used for that purpose to date. This method has the potential to close data gaps and extend existing ice draft time series in all ice-covered regions and supports the validation of sea ice thickness products from satellite missions such as CryoSat-2, SMOS or ENVISAT.
Highlights
Moored Upward-Looking Sonars (ULS) are the primary source for high-resolution and long-duration time series of sea ice draft [1]
In order to overcome the lack of ice draft data in this important source region of Arctic sea ice, we present an adaptive approach to derive ice draft time series from Acoustic Doppler Current Profilers (ADCPs) data that are not based on additional pressure data to determine instrument depth
ADCPs [10], we are able to compare ADCP-derived daily mean ice draft to reference time series based on ULS data
Summary
Moored Upward-Looking Sonars (ULS) are the primary source for high-resolution and long-duration time series of sea ice draft [1]. Compared to standard ULS systems, the inherent instrument setup of upward-looking ADCPs, with a larger beamwidth and default beam angles to the vertical, leads to larger uncertainties in the derived sea ice draft values. This is the case even if the instrument depth is precisely known from pressure measurements and correction terms are applied to overcome the ADCP’s deficiencies [10,12,16]. Ice draft derivations based on ADCP BT data are less common and a way of overcoming
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