Precipitable water vapor estimates from homogeneously reprocessed GPS data: an intertechnique comparison in Antarctica
Thomas, ID and King, MA and Clarke, PJ and Penna, NT, Precipitable water vapor estimates from homogeneously reprocessed GPS data: an intertechnique comparison in Antarctica, Journal of Geophysical Research, 116, (D4) Article D04107. ISSN 0148-0227 (2011) [Refereed Article]
Homogeneously reprocessed GPS data offer the possibility of an accurate, stable,
and increasingly long‐term record of integrated precipitable water vapor (PW) of
particular value in data sparse regions. We present such a global reanalysis of GPS data,
focusing on 12 Antarctic sites. We show stepwise improvements of GPS zenith total
delay (ZTD) estimates upon adoption of each of (1) absolute antenna phase centre
variations, (2) VMF1 tropospheric mapping functions, and (3) an accurate model of
a priori zenith hydrostatic delay (ZHD) from observed surface meteorological data.
The cumulative effect of these three additions to the analysis is a systematic decrease in
the magnitude of GPS estimates of ZTD by an average of ∼11 mm ZTD (∼1.8 mm PW).
The resultant GPS PW data set for 2004 shows a mean bias to radiosonde measurements
of ‐0.48 mm PW. Our conclusion is that, in Antarctica at least, a proportion of the
widely observed bias between GPS and radiosonde measurements can be explained by
earlier GPS analysis deficiencies. We also compare our GPS PW measurements with AIRS
and MODIS level 2 PW products. The GPS agreements with AIRS and MODIS are
comparable. Reanalyzed GPS gives typically larger measurements than AIRS with a
mean site bias of 0.58 mm PW and a mean rms of 1.24 mm PW. By contrast, the GPS
measurements are typically smaller than those from MODIS, with a mean site bias of
‐0.35 mm PW and rms of 1.42 mm PW. PW estimates from reprocessed GPS solutions
using state‐of‐the‐art models now have greater potential for assimilation into regional
or global numerical weather models.