Sensing climate change using the Global Positioning System

Increases in temperature and water vapor in the lower troposphere of the model atmosphere produce opposite effects on the occultation delay. Increased temperature tends to decrease the delay, while increased water vapor increases the delay. Amplified by the long "lever arms" of the LEO-atmosphere-GPS link, a strong "greenhouse warming" signal is simulated, with increases in occultation delay of nearly 100 m using the globally averaged data.

This increase indicates that globally the effect of increased water vapor dominates. However, significant regional differences are present in the occultation delay response. In the tropics, where the temperature increase is smallest and the water vapor increases are largest, increases in delay of about 300 m are simulated.

In contrast, in the polar regions where the increased temperatures are greatest and the increases in water vapor are smallest, the temperature effect dominates and a decrease in occultation delay of nearly 70 m is simulated. When compared to expected errors in measuring the occultation delay of about 1 m, these results indicate that monitoring trends in occultation delays would be a practical way to detect global and regional climate change.