Presenters from the AIRS Validation Team and AIRS Science Team and the
AIRS Validation Team discussed both in situ observational methods, and
interpretation of those observations when compared with AIRS. Major
emphasis was on the measurement of upper tropospheric humidity, and the
interpretation of those measurements.

*Holger Voemel* discussed the different methods for measuring upper
tropospheric water vapor using balloon-borne sensors. He contrasted the
measurement sensitivity of the NOAA/CMDL frostpoint hygrometer, the
Vaisala Humicap sensor and the Snow White system, and showed that each
system required careful interpretation.

*David Whiteman* discussed the measurement of water vapor and
temperature using his Raman lidar and a mix of other instruments for 41
overpasses between September 2002 and January 2003. He showed many
intercomparisons between lidar and other systems, especially
radiosondes. Intercomparison with Chris Barnet's developmental AIRS
retrieval algorithm results illustrated the importance of understanding
the meteorological context of each match-up, especially cloud state.

*Roberto Calheiros* described activities in Brazil to validate the HSB
observations. Many of these resulting measurements will be useful for
validation of AIRS products.

*Von Walden* described his measurements taken from Dome Concordia,
Antarctica, during January during 106 Aqua overpasses. He showed some of
the unusual features of infrared spectra associated with these cold, dry
conditions. He also described some the challenges of interpreting these
observations, including surface shadowing of wind-carved snow, very low
water vapor, and a strong diurnal cycle.

*Frank Schmidlin* briefly described the measurements his team had
acquired to date. These included 76 ozonesondes, 28 chilled mirror
sondes, rocketsondes, and standard radiosondes.

*Hank Revercomb* showed a radiance intercomparison between AIRS and the
aircraft-borne SHIS instrument. Taking advantage of unusually clear
conditions in November over the Gulf of Mexico, he showed that the two
instruments agree with one another to within their measurement
uncertainties. These differences are of order 1 K.

*Ralf Bennartz* described the ground validation of AMSU and HSB rainfall
products at high latitude using the BALTEX radar system over
Scandinavia. He described some the challenges of this intercomparison,
including careful consideration of radar beam geometry, and radar
calibration uncertainties of roughly 50 %.

*Phil Rosenkranz* described comparisons of AMSU and HSB radiances with
those calculated using ARM and operational radiosondes. The data set of
several hundred radiosondes revealed significant biases associated with
instrument sidelobes.

*Wallace McMillan* described AIRS validation activities associated with
the ABOVE experiment on the Chesapeake Light Platform. He showed
intercomparisons of developments retrievals and temperature, water vapor
and cloud properties. He also described activities to measure carbon
monoxide during the next round of ABOVE experiments

*Larrabee Strow* described the validation of the AIRS forward model
using observations from ECMWF, the ARM sites, and from AIRS-dedicated
experiments. He showed that those biases varied with total water vapor.
He also showed maps of biases against ECMWF in shortwave window
channels, apparently associated with a low level haze of small
particles.

*Peter Minnett* described the observations available from instrumented
ships. These include downward and upward looking infrared radiances,
total water vapor from an uplooking microwave radiometer, and
temperature and water vapor from radiosondes.

*George Aumann* described the comparison between RTG SST reanalyses and
inferred SST observed at the AIRS 2616 wavenumber channel. He described
his method for detecting cloud-free footprints, and showed maps and
histograms of differences between the two data sets. The maps revealed
large, coherent regions where AIRS is biased cold, suggesting a thin
haze or aerosol layer over ocean.

*Eric Fetzer* described an initial case study for a very clear night at
the ABOVE experiment at the Chesapeake Bay Light platform. This showed
very good agreement between retrieval and sonde, and that the brightness
temperatures in the AIRS shortwave infrared were consistent with
regional ECMWF SST reanalyses.