Measurement analyses and evaluations of sea-level heights using the HY-2A satellite's radar altimeter

The HY-2A satellite is China’s first independent oceanic dynamic environmental satellite, and has been operating continuously for more than six years. The satellite’s radar altimeter, which is one of the main loads on the satellite,has the ability to realize all-weather and all-day observations of global sea-surface heights, as well as significant wave heights and sea-surface wind speeds. These observed data have been widely used in marine disaster prevention and reduction, along with resource development, maritime security and other fields. In order to achieve a comprehensive understanding of the multi-year overall observational performances of the HY-2A satellite’s radar altimeter, all of the observational data of the IGDR product from October 26, 2012 to August 27,2017 were selected in this study for a comprehensive evaluation. The height measurement capability of the HY-2A satellite’s radar altimeter was evaluated using self-crossover and Jason-2 crossover methods. The height discrepancies at the self-crossover point of the HY-2A satellite’s ascending and descending orbits were also calculated. It was found that for the HY-2A satellite’s radar altimeter in global waters under the restriction conditions of ascending and descending orbits, the height anomaly differences were within a range of less than 30 cm. The absolute mean error was determined to be 5.81 cm, and the height anomaly standard deviation was 7.76 cm. Under the conditions of the observational areas being limited within a scope of 60° from the Equator, it was determined that the sea-level height anomaly differences were less than 10 cm at the junction of the ascending and descending orbits, the absolute mean error was 3.95 cm. In addition, the sea-level height anomaly standard deviation was observed to be 4.76 cm. Using a mutual cross method with the Jason-2 satellite, it was found that under the conditions of the observational area being within the scope of 66° from the equator, the height anomaly differences at the junction were less than 30 cm, and the absolute mean error of HY-2A and Jason-2 sea level height anomaly was 5.86 cm, with a standard deviation of 7.52 cm. It was observed that, if within the sea area the sea level height anomaly difference was limited to within 10 cm, then the absolute mean error and standard deviation could reach 4.19 cm and 4.98 cm, respectively. It was confirmed that the HY-2A satellite’s radar altimeter had successfully reached the height measurement level of similar international altimeters. Therefore, it had the ability to meet the needs of marine scientific research and ocean circulation inversions.