Infrared satellites

Satellite images can reveal information about crop growth and potential pest infestation. The darker areas of this infrared satellite image show where corn growth has been stunted by some form of infestation. 

NASA s Infrared Astronomy Satellite (IRAS), which was launched in 1985, consisted of a liquid-helium cooled telescope (60-cm mirror) and produced the first all-sky maps of the infrared universe at 25, 60, and 100 pm wavelength. IRAS was followed in 1996 with another cooled telescope in space, the Infrared Satellite Observatory (ISO), an ESA mission, which was a true observatory that could carry out follow-up observations of the IRAS sources. In 2003, NASA s Spitzer Space Telescope, with an 85-cm mirror, achieved major advances in sensitivity, image quality and field-of-view over ISO. Although its mirror was only slightly larger than ISO s 60-cm mirror, the use of new, sensitive, and large-area infrared array detectors has permitted this new view of the infrared universe. 

It is used in coinage and is a standard for monetary systems in many countries. It is also extensively used for jewelry, decoration, dental work, and for plating. It is used for coating certain space satellites, as it is a good reflector of infrared and is inert. 

The Advanced-Very-High-Resolution Radiometer (AVHRR) carried on board the NOAA-7 satellite has been collecting radiance data from the earth s surface since 1978. The polar-orbiting satellite records global data on a neardaily basis. The 4-kilometer data have been remapped by NO A A into monthly composites. The data are collected in 2 bands-one visible (VIS), the other near infrared (NIR). The Normalized Difference Vegetation Index, or NDVI, defined... 

On the last three decades, several space experiments with parts at very low temperatures have been flown. Among these, we mention IRAS (Infrared Astronomical Satellite) launched in 1983 (see Fig. 14.1), COBE (Cosmic Background Explorer) launched in 1989, ISO (Infrared Space Observatory) launched in 1995 and Astro-E (X-ray Observatory), launched in 2000 with instrumentation at 65 mK [35], Some cryogenic space missions are in the preparation or in final phase in Europe, USA and Japan. For example, ESA is going to fly Planck (for the mapping of the cosmic background radiation) and Herschel (called before FIRST Far Infrared and Submillimetre Telescope ) [36], These missions will carry experiments at 0.1 and 0.3 K respectively. 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

An average of temperature records on the earth s surface over a year indicates that the earth s average surface temperature is about 14°C (57°F). But, the earth s 240 watts per square meter of thermal infrared radiation as measured by satellite is equivalent to the radiation emitted by a black body whose temperature is about -19°C (-3°F), not the 14°C (57°F) average measured at the earth s surface. The 33°C (60°F) difference between the apparent temperature of the earth as seen in space and the actual temperature of the earth s surface is attributed to the greenhouse effect. 

Infrared spectra, see also specific compounds aluminum hydrides, 41 223 of bipy and phen complexes, 12 159-162 of borates, 25 200-201, 203, 205-206, 211 of carbonyl complexes, satellite bands, 12 ... 

Clearly, 254 K is much colder than the typical temperatures around 288 K (15°C) found at the earth s surface. This difference between the calculated effective temperature and the true surface temperature is dramatically illustrated in Fig. 14.4, which shows the spectra of infrared radiation from earth measured from the Nimbus 4 satellite in three different locations, North Africa, Greenland, and Antarctica (Hanel et al., 1972). Also shown by the dotted lines are the calculated emissions from blackbodies at various temperatures. Over North Africa (Fig. 14.3a), in the window between 850 and 950 cm-1, where C02, O-, HzO, and other gases are not absorbing significantly, the temperature corresponds to blackbody emission at 320 K due to the infrared emissions from hot soil and vegetation. 

FIGURE 14-4 Infrared emission from earth measured from the Nimbus 4 satellite (a) over the Niger Valley, North Africa (14.8°N, 4.7°W) at 12 00 GMT (b) over Greenland (72.9 LN, 41.1°W) at 12 18 GMT, and (c) over Antarctica (74.6°S, 44.4°E) at 11 32 GMT. Emissions from blackbodies at various temperatures are shown by the dotted lines for comparison (adapted from Hanel et at., 1972). 

These weaker bands can have significant effects on the calculated outgoing infrared radiation. For example, Ho et al. (1998) show that much of the reported discrepancy between modeled outgoing long-wavelength radiation and satellite measurements can be attributed to not including weaker absorption bands due to C02 at 4.3 /xrn and 03 at 14 pm and the weaker O, lines located far from the center of the strong 9.6-pm band. 

In the paper of Brato2, Had i and Sheppard [9] some papers are mentioned dealing with the infrared absorption spectra in which such satellites have been observed. The frequency differences of the latter and the fundamental 0—H band are about 200-100 cm"1 which corresponds to the frequencies of the intermolecular vibrations. It should be pointed out that on the basis of thermodynamics. Harford [10] has obtained for the hydrogen bond frequency a value of the order of approximately 200 cm-1. 

Figure 10.13 The structure and infrared spectrum of/m 5-[C5H5Fe(CO)2] . (The two weaker bands are l3CO satellites.)...

The integrated intensity of the satellite spectrum is very close to that of the trapped electron spectrum. The former spectrum decays concomitantly with the latter either with photo-bleaching with the infrared... 

Measurements either from the ground or from satellites have been a major contribution to this effort, and satellite instruments such as LIMS (Limb Infrared Monitor of the Stratosphere) on the Nimbus 7 satellite (I) in 1979 and ATMOS (Atmospheric Trace Molecular Spectroscopy instrument), a Fourier transform infrared spectrometer aboard Spacelab 3 (2) in 1987, have produced valuable data sets that still challenge our models. But these remote techniques are not always adequate for resolving photochemistry on the small scale, particularly in the lower stratosphere. In some cases, the altitude resolution provided by remote techniques has been insufficient to provide unambiguous concentrations of trace gas species at specific altitudes. Insufficient altitude resolution is a handicap particularly for those trace species with large gradients in either altitude or latitude. Often only the most abundant species can be measured. Many of the reactive trace gases, the key species in most chemical transformations, have small abundances that are difficult to detect accurately from remote platforms. 

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