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Small Satellites Doing Big Work: Measuring Earth’s Atmosphere using GPS

 

 

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Saturday, August 6, 2016

For the last nine years six small micro-satellites known as COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) have provided NOAA with continuous, valuable data through asurprisingly simple yet effective technique called radio occultation (RO).

COSMIC measures GPS radio signals passing through the atmosphere
COSMIC measures GPS radio signals passing through the atmosphere

 

Bigger is always better…right? Well, as it turns out, maybe not for satellites. For the last nine years six small micro-satellites known as COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) have provided NOAA with continuous, valuable data through asurprisingly simple yet effective technique called radio occultation (RO).

Weighing only 155 pounds each, these small satellites detect tiny distortions in Global Positioning System (GPS) radio signals as they pass through the atmosphere.

The GPS signals, the same ones used by you and I use to get to that new pizza place, are sent from high orbiting global navigation system satellites and are received by COSMIC, orbiting much closer to Earth’s surface.

COSMIC continues to receive the radio signal as it passes through the atmosphere until eventually being cut off. Lasting about three minutes, this period is known as an occultation.

COSMIC in the clean room, in preparation for launch.
COSMIC in the clean room, in preparation for launch.

The COSMIC instruments and ground software know the GPS signal characteristics in the vacuum of space. By calculating the effect the atmosphere has on the signal during the occultation, scientists can create a near real-time snapshot of atmospheric conditions, including temperature, pressure, density, and water vapor content, known as soundings. Together, this information provides vital data that are widely used in numerical weather predictions, climate research and meteorological studies.

Radio occultation works in all weather conditions over land and sea, provides global coverage, is relatively inexpensive, and is highly accurate, requiring no calibration. It can also be used to calibrate on-board instruments for other satellites, making COSMIC the ultimate team player.

Originally developed in the 1960s, RO was used by the Mariner 4 satellite as a way of probing Mars’ atmosphere. But, with the completion of the global positioning system in the 1990s it was quickly realized that the same process could be used here on Earth.

Soon after a successful proof of concept in the late 1990s, several RO missions were launched. Of those, COSMIC became the first satellite constellation dedicated primarily to collecting and delivering near real-time RO data.

Launched on April 15, 2006 as a joint effort between the U.S. and Taiwan, COSMIC is now operating six years beyond its design life and is in need of replacement. Enter COSMIC-2, NOAA’s solution to providing continuity and improvement over current GPS RO data.

Designed as a two-orbit mission, COSMIC-2 will employ12 satellites to provide 10 times the number of previous daily occultations and will utilize a much larger navigation satellite system including GLONASS (Russia’s global navigation satellite system) in addition to the U.S.’s GPS.

Artists rendering of a Formosat 7/Cosmic 2 satellite. Credit: SSTL
Artists rendering of a Formosat 7/Cosmic 2 satellite. Credit: SSTL

Consisting of six satellites, COSMIC-2A is expected to launch in 2016. These six satellites will augment the current COSMIC by providing more homogeneous data over the tropics.

COSMIC-2B is expected to launch in 2019 and will consist of an additional six satellites slated to replace the aging COSMIC spacecraft and complete the COSMIC-2 mission.

The COSMIC-2 mission is a partnership among NOAA, NASA, the United States Air Force, and the National Space Organization of Taiwan, with roles and responsibilities distributed among the partners.