Assessing the reliability and validity of satellite altimetry-derived wet delay in peninsular Malaysia

Abstract

Water vapor is known as a gas state of water. The nature of the water vapor is invisible, which means it cannot be seen but can be sensed by the humidity in the air. As the climate is warming due to the increase of carbon dioxide and other anthropogenic greenhouse gases, water vapor is expected to increase rapidly as models broadly conserve relative humidity. Water vapor consists of two components, namely, dry and wet delay. Only wet delay will be highlighted in this study due to which the dry delay can be modeled easily. The wet delay in the atmosphere needs to be monitored as to detect and predict changes in earth’s climate particularly for weather forecasting. There are many methods that can be used to measure the wet delay such radiosonde and Global Positioning System (GPS). But both of them had their limitations; for example, they were point-based solutions means that the wet delay can be derived at a certain area. Radiosonde method needs to be launched twice daily, and for a single launch, cost a lot. This study presents an effort to extract the wet delay measurement from radiometer system using satellite altimeter. The advantage of using satellite altimeter is that the wet delay parameter can be retrieved on land and marine areas. Thus, it can improve the spatial resolution for wet delay retrieval. This study employs the altimetry-derived wet delay trend based on multi-mission satellite altimeter in the Peninsular Malaysia for 1-year data, in 2014. Two altimeter missions were used, namely, Jason-2 and Saral. Radar Altimeter Database System (RADS) was used to extract the water vapor data. Altimetry-derived water vapor was verified with GPS-derived Zenith Wet Delay (ZWD) at six GPS Continuously Operating Reference System (CORS) stations. The verification results showed that the RMSE between the altimetry-derived wet delay and GPS-derived wet delay was about 3–12 cm. Furthermore, the data from the satellite altimeter is in a good shape with the seasonal variation of precipitation according to the climatic classification of the region. Besides that, the observed data also give reasonable values when considered for the wet and dry seasons because the value from the CORS and satellite altimeter only had a slight difference. In conclusion, altimetry-derived wet delay is promising to be used in climate and weather research in the future.