Global sea surface air pressure observations with V-band O2 differential absorption radar

Observed meteorological data are essential for initialization, adjustment, assimilation, and prediction of numerical weather prediction (NWP) models and influence daily activities of people and society. Many key weather variables such as temperature, humidity and winds are well observed globally by combined surface weather stations and suborbital and orbital remote sensing platforms of current Earth Observing System (EOS). However, sea surface air pressure is a significant observational gap in the current EOS. There is no operational remote sensing method available for this crucial dynamic variable of the Earth’s climate and weather systems. Over open oceans, the pressure can only be observed by in-situ sensors of very limited buoys, ships, and oceanic platforms. Studies find that accurate sea level pressure (SLP) measurements can significantly improve not only dynamics but also thermodynamics, such as temperature fields of NWP models [1]. Weather forecasts, especially severe weather predictions including hurricanes, can also be improved considerably with pressure measurements.

This study presents the SLP retrieval with emphasis on the evaluation of potential impacts of instrumental and environmental uncertainties on the retrievals for measurements of V-band O₂ differential absorption radar systems operating at three spectrally even spaced close frequency bands (65.5, 67.75 and 70.0 GHz). This study finds that precise knowledge on instrument attitude in current design will result in negligible retrieval errors. The spectral control of the instrument and the knowledge on frequency changes will provide accurate information for forward radiative transfer calculations and then, SLP retrieval. Furthermore, the retrieval algorithm combining all three channels, i.e., the 3-channel approach, can effectively mitigate major atmospheric (e.g., water vapor and cloud) and sea surface influences on sea surface air pressure retrieval.

The major uncertainty for sea surface pressure retrieval is caused by the noise in radar power returns for the current design. Analysis demonstrates the potential of global SLP observation with error similar to that of marine in-situ measurements (about 1 ~ 2 mb), which is urgently needed for improvement of NWP models. Currently, NASA is developing an airborne system for demonstration of space applications.  Our presentation will provide more details on the system, SLP retrieval and their applications.

 

Reference

[1] Prive, N., M. Mclinden, B. Lin, I. Moradi, M. Sienkiewicz, G. Heymsfield, and W. McCarty, “Impacts of marine surface pressure observations from a spaceborne differential absorption radar investigated with an observing system simulation experiment”, J. Atmos. Oceanic Tech., 40, 897 – 918, 2023.