Science Spotlight

Station V191


The GPS measurements are made from an instrument container suspended beneath a balloon that flies 10.5 miles above the Earth. Photo credit: Philippe Cocquerez, Centre National d'Etudes Spatiales (CNES).


Name: Balloon
State: Antarctica
Country: Antarctica
Elevation: 16.0 m
Lat/Long:  -74.1341 / -94.33

Balloon Experiment in Antarctica

Global warming is changing the distribution of ice on the Antarctic continent and surrounding oceans, and having impacts on sea level and coastal ecosystems. Few measurements are available in the Antarctic atmosphere to provide a guide for how weather forecasts are performing, and the accuracy of information going into climate models. We have developed a system that uses GPS technology to measure profiles of the temperature of the atmosphere in Antarctica from stratospheric balloons (Figure 2). The GPS signals do not travel exactly at the speed of light; the signals are slowed by the atmosphere as they travel from the GPS satellite to the receiver on the balloon. Larger delays in the signals are due to cooler moister air, so detecting these delays and turning it into information on temperature provides useful data for weather models.

As part of the CONCORDIASI research project in 2010, instrument packages (Figure 1) on two balloons were released into the atmosphere above McMurdo Research Station in Antarctica to an altitude of 17 km, or about 10 1/2 miles above the surface. They were then carried west around the Antarctic continent by the winds of the polar vortex. For more than 50 days, the balloons circulated around the continent, continuously measuring GPS signal delays, which are then turned into vertical profiles of temperature.

This new technique has been shown to provide measurements that agree with conventional temperature sensors that measure temperature profiles directly from balloons, called dropsondes. Only a limited number of dropsonde measurements can be made by a balloon, however, since a balloon can only carry and release 50 such sensors. The new GPS technique can measure profiles continuously as long as the data can be transmitted back to research laboratories by satellite. It will provide valuable information for assuring the accuracy of atmospheric models.

The Antarctic GPS measurement project was a joint effort between lead researcher Dr. Jennifer Haase at Scripps Institution of Oceanography, and the Laboratory of Dynamical Meteorology in Paris, the French weather agency Meteo-France, the French Space Agency CNES, and the larger CONCORDIASI collaboration for the International Polar Year funded in part by the National Science Foundation.

Figure 1.The instrument package that we deployed on the balloon. The white panels on the top of the instrument are the GPS antennas.

 

Figure 2.The GPS radio occultation concept is shown here. A receiver on the balloon measures the signal from a GPS satellite as it sets beyond the horizon. The signal is delayed and refracted as it passes nearly horizontally through the atmosphere becaues it is not a vacuum. With assumptions on spherical symmetry, we can attribute the signal refraction and bending to the properties at the point of closest approach to the surface. In this way we can derive a profile of refractivity through the atmosphere.


Last modified: 2019-12-26  16:24:49  America/Denver  

 

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