Wet path delay (WPD), required to correct sea-level measurements from satellite altimetry, is routinely estimated using observations from onboard microwave radiometers (MWR). However, when MWR retrievals are invalid or absent, WPD is generally obtained from atmospheric models, unless observations from external sources, such as scanning imaging radiometers, are available in spatial and temporal proximity to the altimeter measurements. These external observations, however, provide total column water vapor (TCWV) rather than WPD, and a reliable TCWV-to-WPD conversion is necessary. Current state-of-the-art conversions use TCWV only or TCWV and near-surface air temperature. The first approach is particularly relevant when external sources provide TCWV only. In this context, this paper presents, first, a comprehensive intercomparison of the methods available in the literature and, second, an improved TCWV-to-WPD conversion. The results show that one of the existing functions underestimates WPD by up to 1.6 cm in regions of high water vapor content, while another provides accurate WPD values only under specific atmospheric conditions. This study proposes an updated methodology that yields accurate WPD across the entire TCWV range, highlighting the importance of a reliable TCWV-to-WPD conversion for accurate sea-level estimation when valid MWR observations are unavailable.
Vieira et al. (Sat,) studied this question.