Assessing SARAL/AltiKa Data in the Coastal Zone: Comparisons with HF Radar Observations

Abstract

We present an initial assessment of SARAL/AltiKa data in the coastal band. The study focuses on the Ibiza Channel where the north-south water exchanges play a key role in controlling the circulation variability in the Western Mediterranean. In this area, the track 16 of SARAL/AltiKa Downloaded by [New York University] at 03:55 27 May 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT2 intercepts the domain covered by a coastal high-frequency (HF) radar system, which provides surface currents with a range up to 60 km. We evaluate the performance of the SARAL/AltiKa Ssalto/Duacs delayed-time along-track products when compared to the HF radar surface velocity fields. SARAL/AltiKa data are retrieved at a distance of only 7 km from the coast putting in evidence the emerging capabilities of new altimeter.The derived velocities resolved the general features of the seasonal mesoscale variability with reasonable agreement with HF radar fields (significant correlations of 0.54), However, some discrepancies appear, which might be caused by ageostrophic velocities as well as inaccurate corrections and editing in the altimeter data.Root mean square (rms) differences between the estimated SARAL/AltiKa and the HF radar velocities are of about 13 cm/s. These results are consistent with recent studies in other parts of the ocean applying similar approaches to Topex/Poseidon and Jason-1 missions and using coastal altimeter corrections.

Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

“…Troupin et al (2015) compared ocean currents derived from SARAL/AltiKa altimetry, HF radar and glider measurements and found a good agreement between altimeter and glider currents, as close as 10 km from the coast. Similar results were also found by Pascual et al (2015), with further improvements foreseen from dedicated near-coast instrumental algorithms and geophysical corrections. Birol and Niño (2015) compared Jason-2 and SARAL/AltiKa data in coastal areas of the north-west Mediterranean Sea.…”

The Benefits of the Ka-Band as Evidenced from the SARAL/AltiKa Altimetric Mission: Scientific Applications

“…Among the various alternative sensors available, coastal High Frequency Radar is unique as it provides synoptic, high frequency and high resolution data at the boundary between the ocean and the atmosphere [12]. Here, we build up on a previous study [13] aimed at evaluating SARAL/AltiKa data in the coastal ocean (7-60 km from the shore). In that study, the altimeter performance was evaluated in the Ibiza Channel (Western Mediterranean) by estimating geostrophic currents and comparing them to high frequency (HF) radar surface velocities.…”

“…The period of study is 18 April 2013 to 8 May 2014. The same processing as in [13] is applied for HF radar and as well as for both SARAL/AltiKa and Jason-2 missions. Surface geostrophic velocities from altimetry are computed by finite differences applied to the Absolute Dynamic Topography (ADT), which is obtained by adding SLA and the SMDT-MED2014 Mean Dynamic Topography [14]).…”

Some considerations about coastal ocean observing systems

“…Altimeters can suffer from errors because of inaccuracies in the wet tropospheric correction, land contamination, and tracking uncertainties-all of which are accentuated closer to the coast. Accounting for these sources of error with enhanced algorithms allows for custom-processed coastal altimetry data sets that can now extend to within 10 km of the coast (Vignudelli et al 2011;Pascual et al 2015) with reasonable uncertainties provided that sufficient signal is present (Vignudelli et al 2005). Thus, satellite altimetry is a potentially important coastal data set, especially when other means are not available for measuring variability in remote locations.…”