Three weeks ago, the National Research Council released a report highly critical of the current state of NASA's Earth-observing satellite system. In the report, the scientists on the NRC panel mentioned six missions that the space agency had either delayed or cancelled that the panel believed were vitally important to the future of Earth science. I wrote about this at the time and described in modest detail the first of these six missions mentioned: the Global Precipitation Measurement (GPM) mission, which has been delayed until no earlier than 2010.
The second mission mentioned by the NRC report is called GIFTS, for Geosynchronous Imaging Fourier Transform Spectrometer. Like GPM, GIFTS is essentially all about gathering lots and lots of data, at rapid time intervals and over a large fraction of the Earth's surface. After all, we cannot increase our understanding of the Earth's weather and climate system without thorough knowledge of all its complexity. And that takes boat loads of data, taken at frequent time intervals across large fractions of the Earth's surface, from the remotest mountaintop to the middle of the oceans. Going up into space and looking back down on Earth is the only practical way to obtain such complete data.
Unlike the multi-satellite GPM mission, whose focus was very broad, aiming to improve weather forecasting, climate modelling, hydrological information, and more with its measurements of rainfall and cloud structure, the single satellite GIFTS mission is simply about improving weather forecasting, with a special focus on severe storms. The data it gathers will allow for the determination of three-dimensional, high-resolution information on atmospheric temperature, water vapor, and winds.
Sitting in a geostationary orbit, 22,000 miles up, revolving around the Earth in lockstep with the planet's rotation, the satellite will be able to continuously monitor a large area of the Earth's surface. This continuity of its data is crucial, as it will allow scientists to study the development and rapid changes associated with severe weather events. This is not available at the moment, as such high-resolution data as GIFTS will gather is currently only available via low Earth-orbit satellites that pass over specific locations only every twelve hours or so, or by repeated flyovers by aircraft carrying special instruments.
Much new technology is involved in the instrumentation for this mission, as well as new measurement concepts that will allow the determination of winds at various heights in the atmosphere via the water vapor data. The GIFTS mission is supposed to allow the scientists and engineers to work out the kinks of this new technology, which can then be incorporated into the next round of geostationary weather satellites, GOES-R, slated to be launched starting in 2012.
GIFTS is an imaging spectrometer, as its name implies, which means that it can take spectra at many different points, thus assembling an "image" of spectra. The spectral range covered by the GIFTS spectrometer is in the infrared region, covering wavelengths of radiation from 4.4 to 6.1 microns and 8.8 to 14.6 microns, as shown by the blue bars in the spectrum at right. (For comparison, visible light covers a range of wavelengths from around 0.4 to 0.7 microns.)
The information on temperature and humidity comes from studying how much light is absorbed by water vapor at specific wavelengths. Thanks to all the various rotation and vibration modes possible in an asymmetric molecule such as water, and to the rules of quantum mechanics, water absorbs light (photons) at numerous specific wavelengths in this spectral region. The energy from the photon absorbed goes into pushing the water molecule into a slightly higher-energy rotation or vibration mode. With the significant amount of water vapor in the Earth's atmosphere, numerous spectral features are thus apparent at these wavelengths.
A few other molecules, in particular the pollutants and greenhouse gases carbon monoxide (CO) and ozone (O3) also have spectral features in this region. So the GIFTS instrument will be able to study the distribution and transport of these pollutants as well.
From the point of view of an astronomer, as I used to be, this spectral region is extremely difficult to observe from the Earth's surface. Precisely because of all those water vapor features, faint light coming through the atmosphere from distant, astronomical objects gets absorbed and never makes it to the detectors Going up to the tops of tall mountains such as Mauna Kea in Hawaii helps, but going into space, completely above the atmosphere and all its water vapor, is much better. Hence the motivation for infrared space telescopes such as the relatively new Spitzer Space Telescope.
From the point of view of an atmospheric scientist, however, all those water vapor spectral features are hardly an annoyance—they are where the action is. The motivation for going into space to observe them is simply to get a wide view of much of the Earth at a single time.
Despite over $100 million already spent on developing GIFTS, bringing it near to completion, and an international effort led by the World Meteorological Association to test GIFTS in space, NASA has terminated funding for this mission beyond this year. The National Research Panel instead "recommends that NASA and NOAA complete the fabrication, testing, and space qualification of the GIFTS instrument and that they support the international effort to launch GIFTS by 2008."
I haven't been keeping up. Maybe you can point me in the right direction. Is the idea that NASA wants to redistribute its resources toward mars and moon missions, at the expense of missions that collect scientific information about our own planet? If so, how does NASA justify that decision, given global warming and other earth-based pollution issues that are poorly understood, but that may threaten the health and safety of humankind? If not, then what's up?
Posted by: LoB | May 17, 2005 at 01:56 PM
Yes, that's the basic idea. A vague goal of future human exploration of the Moon and Mars is taking precedence over pre-existing scientific projects. I covered this in a couple earlier posts that may be helpful, here and here.
The justification, according to NASA, is Bush's (underfunded) Moon/Mars directive. The excuse is that NOAA and other agencies will take up the slack. Of course, NOAA has no money to do so, as certain congressmen pointed out a few weeks ago (and as covered in the first of my earlier posts).
This administration's antipathy to science in general and anything related to global warming, in particular, is also well documented. So I don't think it's surprising that Bush's NASA has targeted Earth science missions for squeezing.
Posted by: Peter | May 17, 2005 at 02:23 PM
Studying and knowing anything about nasa is always be interesting and useful keep posting like this...!
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