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Abstract:
Lake Issyk Kul in Kyrgyzstan is a large high-altitude inland lake but ice-free the year around. Due to its E-W extension of ~170km all active radar altimetry missions cross this lake. Since 2016 CAIAG (Kyrgyzstan) and GFZ Potsdam (Germany) installed five GNSS-controlled tide gauges and climate monitoring stations at the lake. The lake surface is neither influenced by ocean tides nor by inverse barometric effects. Tide Gauge data is sampled every minute and climate data, such as wind or air pressure, every five minutes.
Starting in 2017 we performed ship-based lake surveys with GNSS/radar for profiling the lake surface along the satellite passages. With the connection to the gauges, we are able to reconstruct the instantaneous lake profile in ITRF for any altimeter passage. We analyzed the 20Hz GDR Level 2 data of Jason-3 and Sentinel-6 (STC/NTC both LRM/SAR). 2022 we performed surveys along the 35-day (ERS-1, ERS-2, ENVISAT, AltiKa) and GFO-1 orbits. Along each pass stretching up to ~60km we testing all retracker available. We estimated the individual retracker offsets and the internal accuracy. For, e.g., Sentinel-6 the SAR-OCOG retracker performs best (revision F02 onward) after applying an offset of more than 33cm in respect to the GNSS reference pass. For Jason-3 (Rev. F) the OCOG also performs best with an offset of ~19cm.
Our analyses show the capability of the Lake Issyk Kul observatory for the short-latency monitoring of radar altimetry missions as well as for the performance control of all altimeters starting with ERS-1 in 1992.
