Approaches to detection of geochemical stress in vegetation

Work has been carried out to elucidate fundamental relationships between spectral properties of plants and geochemical stress, and a programme of field and laboratory work is in progress. The most significant results and conclusions at this stage are described and attention is focused on the new concepts for stress detection which have been generated. The applications of the research are relevant to the understanding of current remotely sensed data as well as relating to ideas for new instrumentation.     

The infrared imaging channel of the IKS instrument for detection of Comet Halley nucleus

The imaging Channel of the IKS Instrument placed on board the Vega fly-by probes will perform measurements of the infrared emission of the central region of Comet Halley at distances in the 10⁴ ? 10⁵ km range. An encoding wheel analyses one spatial frequency of the infrared image during the whole fly-by. Inversion of this measurement will give low resolution brightness profiles of the nucleus and its immediate surroundings, in two wave-length bandpasses and in two directions of analysis.     

Studies of vegetation and soils from aerospace measurements

The problem of soil and vegetation recognition with the use of satellite-derived digitized images and sub-satellite spectral brightness measurements at test sites data is discussed. A technique for retrieval of soil humus content is suggested.     

The infrared synthetic spectrum of comet Halley

In order to prepare infrared sounding of comet Halley from the flyby VEGA probes, we have computed the synthetic spectrum between 2.5 and 15 μ of a typical comet at a heliocentric distance of ～ 0.8 AU. The present paper is particularly devoted to the contribution from the cometary gases. For a selection of 20 possible parent molecules, the most efficient excitation process is resonant fluorescence by the solar radiation field. The H₂O, CO, CO₂, CH₄, NH₃ and H₂CO molecules are the best candidates for detection by the IKS infrared spectrometers aboard the VEGA probes. For the water molecule, collisions are too rare to ensure thermal equilibrium in the whole coma ; therefore a limited number of fluorescence lines are expected to be present in the H₂O vibrational bands.     

Planned NASA space infrared astronomy experiments

A summary is presented of the present status of the NASA space infrared astronomy program. Projects described include the Infrared Astronomy Satellite (IRAS), Small Infrared Telescope on Spacelab 2 (IRT), Cosmic Background Explorer (COBE), Shuttle Infrared Telescope Facility (SIRTF), Space Telescope (ST), and the Large Deployable Reflector (LDR). The important technical developments achieved in these programs are also discussed, as well as critical needs for future missions.     

Advances in infrared and sub-millimeter filters

Infrared filters use a large variety of physical principles and techniques, as can be expected since they cover three decades of the IR spectrum (1 μm - 1 mm). The multilayer interference filters, derived from optical techniques, play the main role in the region 1 μm–40 μm. They have been successfully used in space applications. On the other side of the spectrum is the domain of metallic mesh filters, which is still developing. Bulk absorption, Reststrahlen bands, diffusion and gratings are also used to achieve the desired properties. A short review of this situation is given, with emphasis on the present trends and developments.Infrared and sub-millimeter filters use a large variety of physical principles and techniques that we may classify in two large families.     

Using vegetation indices and texture measures to estimate vegetation fractional coverage (VFC) of planted and natural forests in Nanjing city,China

Vegetation fractional coverage (VFC) is an important vegetation parameter affecting exchanges of carbon, water, energy between the atmosphere and surface. In this study, the applicability of tonal and texture measures calculated using an IKONOS_2 image in retrieving VFC of forests was investigated in the urban area of Nanjing city, China. Four spectral vegetation indices (VI) and six texture measures (TEX) were related to VFCs acquired from in situ measurements. Models for estimating VFC based on VIs or/and TEXs were established and validated for planted low broad-leaf forest plots (PLB), planted mature forest plots (PMF), natural broad-leaf forest plots (NBF), and all forest plots (ALLv), respectively. The results show that high spatial resolution remote sensing data is applicable to estimate VFC in urban areas, and TEXs may act as effective supplements of vegetation indices (VIs) for the retrieval of VFC. VIs are suitable for VFC estimation of mature forests (such as NBF and PMF) with high vegetation density, and TEXs can yield a more accurate estimate for planted forests (such as PLB and PMF) with regular spatial distribution if they are calculated with proper parameters, such as window size. The combination of VIs and TEXs improve the estimation of VFC if forest types are not previously differentiated. The results can be used as a reference for determining effective spectral or texture parameters in VFC estimation under similar environmental conditions according to vegetation maturity and regularity.     

Recent infrared observations of comets with UKIRT and IRAS

A preliminary analysis of infrared observations of comets P/Crommelin and P/Tempel 1 is presented. Comet P/Crommelin was observed from UKIRT over the range 1–20 micron, using standard filters. From the shape of the thermal emission spectrum, the temperature of the dust grains is estimated (T = 314 ± ₃₃⁴⁴K) and also the dust production rate (1.3 × 10⁵gs^?1). Comet P/Tempel 1 was observed with the Infrared Astronomical Satellite (IRAS). The emission is found to be considerably extended and there is also evidence for temperature variation of the dust grains as indicated by the 12 to 25 micron flux ratio.     

Rocket-borne measurements of atmospheric infrared emissions by spectrometric techniques

As part of the MAP/WINE Campaign 1983/84 a liquid helium cooled infrared grating spectrometer measured night zenith radiances of CO₂, O₃, and H₂O in the mesosphere and lower thermosphere. From a comparison of the measured spectral radiances with results from LTE radiative transfer calculations atmospheric temperatures and concentration profiles of H₂O and O₃ were determined, showing some interesting features. The ozone densities obtained appear to contradict model predictions based upon the assumption that ozone is in photochemical equilibrium at mesospheric heights. Since the ozone density distribution shows quite similar structures as the vertical wind profile, transport effects seem to play a major role in the mesospheric ozone formation.     

Near infrared observations of comet Halley from Vega 2

Spatial distribution of the continuum radiation in the range of 0.95–1.9 μm presumes total dust production rate of the comet of 10ρ tonne s⁻¹ (ρ is the dust material density) and its angular distribution proportional cos . Observations of the water vapor band at 1.38 μ m reveal strong jets, their time shift from the dust jet measured in situ is consistent with gas velocity of 0.82±0.1 km s⁻¹ and dust velocity of 0.55±0.08 km s⁻¹. The OH vibrational-rotational bands observed are excided directly via photolysis of water vapor. Water vapor production rate deduced from the H₂O band and OH band intensities is 8×10²⁹ s⁻¹. Intensity of the CN(0,0) band result in the CN column density of 9×10¹² cm⁻², i.e. larger by a factor of 3 than given by the violet band.     

Girl — the German infrared laboratory for spacelab

GIRL is a liquid helium cooled 50 cm telescope equipped with four focal plane instruments dedicated to astronomical and aeronomical observations. These instruments, a detector array, a photopolarimeter, an Ebert-Fastie-spectrometer and a Michelson-interferometer make up an “infrared observatory” having high sensitivity and high spectral and spatial resolution. Si:Ga-, Si:Sb-, Si:As-, Si:P-, Ge:Be-, Ge:Cu- and Ge:Ga-detectors with NEP-values as low as $\text{3 10}{}^{\mathrm{?17}}\text{W Hz}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$ have been tested and will be used to cover the wavelength range 3…120 μm. A full size “thermal model” of the GIRL cryostat containing 300 1 of superfluid helium at 1.6 K has been tested at the industrial prime contractor MBB; results of these tests will be presented in a following paper by F. Dahl et al. Several new techniques for cold telescopes are used in GIRL, for instance a glass ceramics primary mirror, a low power chopping secondary and an active helium phase separator. The scientific objectives include studies of star formation regions and active galaxies as well as measurements of spurious gases in the earth atmosphere. GIRL will be pointed by the Instrument Pointing System (IPS) and is scheduled to fly on Spacelab in 1986/87.     

Scientific results from the pioneer Saturn infrared radiometer

The Pioneer 11 Infrared Radiometer instrument made observations of Saturn and its rings in broadband channels centered at 20 and 45 μm and obtained whole-disk information on Titan. A planetary average effective temperature of 96.5±2.5 K implies a total emission 2.8 times the absorbed sunlight. Correlation with radio science results implies that the molar fraction of H₂ is 90±3% (assuming the rest is He). Temperatures at the 1 bar level are 137 to 140 K; regions appearing cooler may be overlain by a cloud acting as a 124 K blackbody surface. A minimum temperature averaging 87 K is reached near 0.06 bars. Ring boundaries and optical depths are consistent with those at optical wavelengths. Ring temperatures are 64–86 K on the south (illuminated) side, ～54 K on the north (unilluminated) side, and at least 67 K in Saturn's shadow. There is evidence for a south to north drop in ring temperatures. Titan's 45 μm brightness temperature is 75±5 K.     

Equatorial cloud properties on Venus from pioneer orbiter infrared observations

Infrared observations of Venus from the Pioneer Orbiter have been used to study the limb darkening properties of the cloud tops at wavelengths and spatial resolutions not previously attained. The preliminary results show evidence for an extensive haze feature over the equatorial morning terminator and for small amounts of a far-infrared absorber concentrated near local noon, also near the equator. The evidence for these features is reviewed and their possible origins briefly discussed.     

Landsat monitoring of desert vegetation growth, 1972–1979 using a plant-shadowing model

Landsat digital data spanning the period 1972–1979 were analyzed to monitor the status of vegetation within and outside an exclosure in the northern Sinai (precipitation 100–150 mm/year). This 6×6 km exclosure was fenced off in the summer of 1974 and subsequently has been free from the anthropogenic pressures (overgrazing, cultivation in small fields, and harvesting of dry plants as firewood) that continued outside the exclosure. The recovery of the ecosystem within the exclosure is monitored applying a previously tested model. The model quantitatively describes the reduction in the reflectivity to zenith due to shadowing effects by mostly vertical plants. The darkening (reduction in the reflectivity) in the exclosure was compared to the status before the fencing-off and to the essentially unchanging bare sands outside the exclosure. The vegetation protrusion parameter s (sum of the products of plant height times diameter for a unit area of the surface), calculated from Landsat digital data for the exclosure, increased from essentially zero in 1972 and 1973 to about 0.18 in 1975 and changed only within narrow limits from 1975 to 1979. The s value of 0.18 indicates that if the clumps of the plants protruding from the surface in the exclosure were laid horizontally on the soil, they would cover 18 percent of the area. This parameter provides a quantitative measure of the condition of the ecosystem, but the relation to the total green and/or brown biomass remains to be determined.     

An estimation of the cooling process by infrared radiation in the atmosphere

Two procedure are presented for quantitative estimation of cloud cover (N), type of clouds (C), as well as base of clouds (C_b) and top of clouds (C^t) by using radiosonde data as well as satellite cloud pictures and radiation data. The data obtained in this way can be used as input data in the model for the estimation of the vertical profile of longwave radiative cooling.     

Validation of nimbus-7 temperature-humidity infrared radiometer estimates of cloud type and amount

Estimates of clear and low, middle and high cloud amount in fixed geographical regions approximately (160km)² are being made routinely from 11.5μm radiance measurements of the Nimbus-7 Temperature-Humidity Infrared Radiometer (THIR). The purpose of validation is to determine the accuracy of the THIR cloud estimates. Validation requires that a comparison be made between the THIR estimates of cloudiness and the “true” cloudiness. The validation results reported in this paper use human analysis of concurrent but independent satellite images with surface meteorological and radiosonde observations to approximate the “true” cloudiness. Regression and error analyses are used to estimate the systematic and random errors of THIR derived clear amount.     

Improved rainfall estimation over the Indian region using satellite infrared technique

The GOES Precipitation Index (GPI) technique (Arkin, 1979) for rainfall estimation has been in operation for the last three decades. However, its applications are limited to the larger temporal and spatial scales. The present study focuses on the augmentation on GPI technique by incorporating a moisture factor for the environmental correction developed by Vicente et al. (1998). It consists of two steps; in the first step the GPI technique is applied to the Kalpana-IR data for rainfall estimation over the Indian land and oceanic region and in the second step an environmental moisture correction factor is applied to the GPI-based rainfall to estimate the final rainfall. Detailed validation with rain gauges and comparison with Tropical Rainfall Measuring Mission (TRMM) merged data product (3B42) are performed and it is found that the present technique is able to estimate the rainfall with better accuracy than the GPI technique over higher temporal and spatial domains for many operational applications in and around the Indian regions using Indian geostationary satellite data. Further comparison with the Doppler Weather Radar shows that the present technique is able to retrieve the rainfall with reasonably good accuracy.