CoAuthors

Paolo Cipollini (National Oceanography Centre, United Kingdom); Stefano Vignudelli (CNR, Italy); Josep Coca (University of Cadiz, Spain)

Four and half years of CryoSat-2 SIRAL data in SAR mode (at 18-Hz posting rate) and 2 years of AltiKa SARAL data (at 1 Hz) have been validated using two radar MIROS tide gauges in the Gulf of Cadiz: Huelva (HU), located close to the Tinto-Odiel river system, and Bonanza (BN), at the mouth of the main tributary in the study area, the Guadalquivir River. Tide gauge data were provided by Puertos del Estado (https://www.puertos.es/) at 5-minute interval. Data from CryoSat-2 SIRAL (processed according to baseline B) were provided by the European Space Agency (ESA) Grid Processing On-Demand (GPOD) SARvatore (SAR versatile altimetric toolkit for ocean research & exploitation) service available at: https://gpod.eo.esa.int/. The data selection was made considering the track segments in a radius of 50 km from the tide gauges. AltiKa data, from two exact-repeat tracks in the vicinity of the tide gauge, were obtained from the Radar Altimeter Data System (RADS) available at: http://rads.tudelft.nl/rads/rads.shtml. Time series of Sea Level Anomalies (Cryo_SLA and AltK_SLA) were compared against in-situ SLA data: HU_SLA (Huelva) and BN_SLA (Bonanza). We estimated the root mean square error (rmse) between satellite and tide gauge data. Time series of Cryo_SLA were built selecting the locations at six different along-track distances to the coast: 1 - 3 - 5 -10 -15 - 20 km. Our results show that rmse increases getting closer to the coast at both stations. The rmse at Bonanza is twice than Huelva. The standard deviation observed in the 5-minutes time series at Huelva/Bonanza is 8/18 cm, respectively. This might indicate a larger signal due to the the Guadalquivir River where Bonanza tide gauge is located: part of the difference found between Cryo_SLA and BN_SLA might be attributed to this dynamic, which is concentrated in the estuary mouth and is not captured by the altimeter instrument as no valid Cryo_SLA data were found in that particular zone. The analysis of AltiKa data shows rmse smaller than 8 cm along the track segment close to Huelva station. The rmse is bigger than 18 cm in the track segment around Bonanza station, also suggesting the river output as source of the noise.