Abstract. In this paper we evaluate new retrievals of the deuterium content of water
vapor from the Aqua Atmospheric InfraRed Sounder (AIRS), with aircraft
measurements of HDO and H2O from the ObseRvations of Aerosols above
Clouds and their intEractionS (ORACLES) field mission. Single-footprint AIRS
radiances are processed with an optimal estimation algorithm that provides
vertical profiles of the HDO∕H2O ratio, characterized uncertainties
and instrument operators (i.e., averaging kernel matrix). These retrievals
are compared to vertical profiles of the HDO∕H2O ratio from the Oregon
State University Water Isotope Spectrometer for Precipitation and
Entrainment Research (WISPER) on the ORACLES NASA P-3B Orion aircraft.
Measurements were taken over the southeastern Atlantic Ocean from 31 August to
25 September 2016. HDO∕H2O is commonly reported in δD notation,
which is the fractional deviation of the HDO∕H2O ratio from the
standard reference ratio. For collocated measurements, the satellite
instrument operator (averaging kernels and a priori constraint) is applied
to the aircraft profile measurements. We find that AIRS δD bias
relative to the aircraft is well within the estimated measurement
uncertainty. In the lower troposphere, 1000 to 800 hPa, AIRS δD bias
is −6.6 ‰ and the root-mean-square (rms) deviation is
20.9 ‰, consistent with the calculated uncertainty of
19.1 ‰. In the mid-troposphere, 800 to 500 hPa, AIRS
δD bias is −6.8 ‰ and rms
44.9 ‰, comparable to the calculated uncertainty of
25.8 ‰.