February 25, 2009 NASA Satellite Fails to Reach Orbit By KENNETH CHANG A NASA satellite to track carbon dioxide in the Earth’s atmosphere failed to reach its orbit during launching Tuesday morning, scuttling the $278 million mission. “It’s a huge disappointment to the entire team that’s worked very hard over years and years and really did their best to see it through,” said Charles P. Dovale, the launch manager. “The reason not everyone is able to do this is — it’s hard. And even when you do the best you can, you can still fail. It’s a tough business.” The Orbiting Carbon Observatory lifted off on schedule at 1:55 a.m. Pacific time from Vandenberg Air Force Base in California aboard a four-stage Taurus XL rocket. But three minutes later, during the burning of the second stage, a clamshell section that protects the satellite as it rises through the atmosphere failed to separate as commanded. The third and fourth stages ignited properly, but because of the added weight of the clamshell, the satellite did not reach orbit. It fell back to Earth, landing in the ocean just short of Antarctica. The carbon observatory was to precisely measure levels of carbon dioxide — the heat-trapping gas that is driving global warming — in the air. Scientists had hoped the new data, covering the entire planet, would help them improve climate models and better understand the “carbon sinks” like oceans and forests and that absorb much of the carbon dioxide.Orbiting Carbon Observatory ! CO2 band at 1.61 microns ! O2 band for comparison at 0.76 microns ! CO2 band at 2.06 micronsThermal Basics Revisited ! Recall that radiant temperature is not equal to kinematic temperature (except for a blackbody) ! Emissivity is the ratio of radiant emittance relative to that of a blackbody ! Emissivity is a spectral quantity (it varies with wavelength) ! Materials that have variable emissivity are “selective radiators”Wavelengths At long wavelengths, such as in the microwave region, the relationship between spectral emittance and wavelength can be approximated. wavelength (μm)Dielectric constantSoil!Tb!Snow water equivalent!Soil!Dry!Snow!Wet snow is a strong !absorber/emitter!Snow Emissivity Example Soil!Wet!Snow!(1)!(2)!(3)!dry snow!Atmospheric Effects ! Atmospheric attenuation increases with frequency from 1 to 1000 GHz (wavelengths from 30 cm – 0.3 mm) ! At frequencies less than 50 GHz (wavelengths greater than 6 mm), there’s little effect of clouds and fog on brightness temperature (it “sees through” clouds) ! Thus, PM can be used to monitor the land surface under cloudy conditions ! In atmospheric absorption bands, PM is used to map water vapor, rain rates, clouds! Active - they transmit their own microwave energy (pulses) at a particular wavelength (single frequency) for a particular duration of time - known as pulsed coherent radar. ! They receive the reflected (back-scattered) signal of these transmitted energy pulses. ! They resolve the Earth’s surface obliquely (side-looking). ! They measure: The returned backscatter signal (intensity). The change that has occurred in the wave form as a result of interacting with the Earth's surface (phase). The slant range distance to the feature(s) resolved. Depression Angle Ground range Look Angle Incidence Angle Slant Range: Near and far range Imaging Systems, Active Sensors1. Introduction1. Introduction Radar wavelengths2. Scatterometry ! Scatterometer is a radar system that provides a quantitative measure of the backscattering cross section as a function of the incident angle . Backscatter cross-section is a measure of how detectable an object is with a radar. When radar-waves are beamed at a target, a number of different factors determine how much electromagnetic energy returns to the source, such as the angles created by the surface/plane intersections. ! A scatterometer transmits a continuous signal or a series of pulses and the strength of the returned signal is recorded.Beginnings of Typhoon Hagibis, May 15, 2002Application of Scatterometer3. SLAR and SAR ! There are two types of imaging radar: (1) Side-looking airborne radar (SLAR), and synthetic aperture radar (SAR), has high resolution refinement of the SLAR. 3.1 Imaging3.2 Penetration3.2 Penetration3.3 Resolution3.4 Distortion of the image3.4 Distortion of the image Distorted image Corrected image3.4 Distortion of the image Distorted image Corrected image From what direction was this image
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