Retrieval of water vapor using ground-based observations from a prototype ATOMMS active centimeter- and millimeter-wavelength occultation instrument
2019
Abstract. A fundamental goal of satellite weather and climate observations is profiling
the atmosphere with in situ-like precision and resolution with absolute
accuracy and unbiased, all-weather, global coverage. While GPS radio
occultation (RO) has perhaps come closest in terms of profiling the gas state
from orbit, it does not provide sufficient information to simultaneously
profile water vapor and temperature. We have been developing the Active
Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS) RO system
that probes the 22 and 183 GHz water vapor absorption lines to
simultaneously profile temperature and water vapor from the lower troposphere
to the mesopause. Using an ATOMMS instrument prototype between two
mountaintops, we have demonstrated its ability to penetrate through water
vapor, clouds and rain up to optical depths of 17 (7 orders of magnitude
reduction in signal power) and still isolate the vapor absorption line
spectrum to retrieve water vapor with a random uncertainty of less than
1 %. This demonstration represents a key step toward an orbiting ATOMMS
system for weather, climate and constraining processes. ATOMMS water vapor
retrievals from orbit will not be biased by climatological or first-guess
constraints and will be capable of capturing nearly the full range of
variability through the atmosphere and around the globe, in both clear and
cloudy conditions, and will therefore greatly improve our understanding and
analysis of water vapor. This information can be used to improve weather and
climate models through constraints on and refinement of processes affecting
and affected by water vapor.
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