Remote-sensed spectra

Plate tectonic activity, which is responsible on Earth for subduction zones, spreading centres and obducted ophiolites, as well as associated ore deposits of Cu, Cr and Ni described in 8.6, appears to have been less significant on other terrestrial planets. As a result, local enrichments of these and other transition elements (apart from Fe and Ti) are probably absent on the Moon, Mercury, Venus, Mars and the asteroids. Since Fe and Ti minerals are predominant on terrestrial planets, electronic spectra of Fe2+ and Fe3+ in silicates and oxides influenced by Ti4+ and Ti3+ are expected to dominate remote-sensed spectra of their surfaces. 

Figure 10.6. Remote-sensed spectra of representative areas on the Moon s surface (from Gaddis et al., 1985). Left telescopic spectral reflectance scaled to unity at 1.02 i.m and offset relative to adjacent spectra right residual absorption features for the same measurements after a straight line continuum extending from 0.73 pm to 1.6 pm has been removed, (a) Highland soil sampled at the Apollo 16 landing site (b) high-Ti mare basalt at the Apollo 17 landing site (c) low-Ti mare basalt at Mare Serenitatis and (d) pyroclastic deposits at Taurus-Littrow.

The contrasting temperature-induced shifts of the pyroxene 1 and 2 pm bands could lead to erroneous estimates of the composition and, to a lesser extent, structure-type of a pyroxene-bearing mineral assemblage deduced from the remote-sensed reflectance spectrum of a hot or cold planetary surface if room-temperature determinative curves, such as that shown in fig. 10.5, are used uncritically. For example, remote-sensed spectra of planets with hot surfaces, such as Mercury and the Moon, would lead to overestimates of Fe2+ contents of the orthopyroxenes and underestimated Fe2+ contents of the clinopyroxenes (Singer and Roush, 1985). Planets with cold surfaces, such as Mars and the asteroids, could produce opposite results. On the other hand, the room-temperature data underlying the pyroxene determinative curve shown in fig. 10.5 may impose constraints on the compositions of pyroxenes deduced from telescopic spectra of a planet with very high surface temperatures, such as Mercury. 

P.J. Zarco-Tejada, J.R. Miller, and G.H. Mohammed. Remote sensing of solar-induced chlorophyll fluorescence from vegetation hyperspectral reflectance and radiative transfer simulation, in Fro m Spectroscopy to Remotely Sensed Spectra of Terrestrial Ecosystems, R.S. Muttiah (Ed.). (Kluwer, Dordrecht, The Netherlands, 2002) 233-269. 

Kumar, M. and Monteith, J. L. (1981). Remote sensing of crop growth. In Plants and the Daylight Spectrum" (H. Smith, ed.), pp. 133-144. Academic Press, New York. 

Clay minerals are ubiquitous up to hundreds of metres from hydrothermal U mineralization, and often there is zoning in the type of alteration minerals (Hoeve Quirt 1984). These can be mapped with remote sensing that can detect in the visible and the middle-infrared sections of the electromagnetic spectrum (Earle et al. 1999). The two oxidation states of U and Fe have been proposed to map bleached... 

One of the first examples of the modem application of remote sensing of the composition of the atmosphere was the assertion by Hartley in 1880 that the UV absorption in the solar absorption spectrum was attributable to ozone. In this manner the earth s stratospheric ozone layer was discovered. Since this pioneering work and especially in die past 30 years, there has been rapid progress in the development of atmospheric remote sensing techniques. 

Simonson et al. [148] demonstrated remote detection of explosives in soil by combining distributed sensor particles with UV/vis fluorescence LIDAR technology. The key to this approach is that the fluorescence emission spectrum of the distributed particles is strongly affected by absorption of nitroaromatic explosives from the surrounding environment. Remote sensing of the fluorescence quenching by TNT or DNT is achieved by fluorescence LIDAR - the emission spectra were excited in field LIDAR measurements by a frequency-tripled Nd YAG laser at 355 nm and the fluorescence collected with a telescope and various detector systems housed in a 10 x 50 trailer. TNT has been detected in the ppm range at a standoff distance of 0.5 km with this system (Fig. 16). An important limitation to this technique is the pre-concentration of the explosives on the sensor particles, which requires the presence of water to facilitate the transport of the explosive from the surface of the soil particles to the sensor particles. 

The resulting continuum is very broad, since it could be measured from 230 nm in the ultraviolet to 4.5 pm in the mid-infrared. The combined spectrum is shown in Fig. 15.8. The fast decrease of the spectrum up to 2.5 pm (4 orders of magnitude between 800 nm and 2.5 pm) slows down beyond 2.5 pm, with only one order of magnitude drop between 2.5 and 4.5 pm. On the spectrum, the absorption band of water between 1.8 and 2.5 pm is clearly visible, showing the potential of the white-light for optical remote sensing in the atmosphere. 

The distribution map of Phaeocystis presented here can hardly be improved, not even by ocean colour remote sensing the frequent cloud cover over the North Atlantic hinders satellite-borne observations, but not the CPR survey. Also, the pigment signature of Phaeocystis is not very specific (Antajan et al. 2004) so the absorption spectrum and therewith the light reflectance hardly differs from that of other fucoxanthin- and fucoxanthin-derivative-containing phytoplankton... 

By measuring the chlorophyll fluorescence induction kinetics and the fluorescence spectrum of an intact leaf or plant the condition and potential activity of the photosynthetic apparatus can be estimated (1, ed. H.K. Lichtenthaler). Solely two parameters namely the chlorophyll fluorescence ratio F685/F730 and the fluorescence life time are reliable to measure by remote sensing (2). 

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