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How does the precipitable water derived from GPS data processed with GIPSY software compare to precipitable water derived from GPS data processed with GaMIT software?

This page briefly addresses how the results in this study could be related to what software package is used to process the GPS data. As noted here, there are three well-known software packages that are used worldwide to convert GPS data to precipitable water. Although this study is primarily focussing on GiPSY output, GaMIT output has also been obtained to see if there are any notable differences between the two algorithms. The graph below shows the computed precipitable water from Lamont, OK for several days in August of 1999 (regrettably, the GiPSY data overlaps only for 24 hours). There is good agreement between the two methods.

A measure of how well the two processes match can be gleaned from comparisons at three other stations: Vici, OK, White Sands Missile Range in New Mexico, and Scripps Institute of Oceanography just north of San Diego CA. Admittedly, this comparison is extremely limited; we are trying to secure more GaMIT data and more GiPSY data to produce more comparisons.

Click the image at left to see a time series plot of precipitable water (GiPSY-produced vs. GaMIT-produced) at Lamont, OK.

Click the image at left to see a time series plot of precipitable water (GiPSY-produced vs. GaMIT-produced) at Vici, OK.

Click the image at left to see a time series plot of precipitable water (GiPSY-produced vs. GaMIT-produced) at White Sands Missile Range in New Mexico.

Click the image at left to see a time series plot of precipitable water (GiPSY-produced vs. GaMIT-produced) at the Scripps Institute of Oceanography in La Jolla, CA (just north of San Diego).

One thing that is evident in the four plots above: the GiPSY precipitable water is usually a bit smaller (i.e., it shows less water vapor in the air) than the GaMIT precipitable water. There are times when the reverse is true, but in general, GiPSY is drier.

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