Application potential of SPOT imagery for topographic mapping

The high resolution and good geometric configuration possible with SPOT gives a high potential for the production of 1:100 000 topographic maps. Studies at University College London have investigated this potential with the aid of a simple instrument which will introduce the necessary corrections to level 1b photographic images and orthophotographs and allow stereoscopic viewing of SPOT images and the ability to compile a line map. Accuracy has been investigated by computing ground co-ordinates from image co-ordinates and pixel positions. The methods used and results obtained in this work are described.Work is now going on to investigate the use of digital image processors in the mapping procedures and the use of analytical plotting instruments, and comments on this work and on future developments are made.     

The detection of energetic cometary and solar particles by the EPONA instrument on the Giotto mission

EPONA is an energetic particle detector system incorporating totally depleted silicon surface barrier layer detectors. Active and passive background shielding will be employed and, by applying various techniques, particles of different species, including electrons, protons, alpha particles and pick-up ions of cometary origin may be detected over a wide spectrum of energies extending from the tens of KeV into the MeV range.

The instrument can operate in two modes namely (a) in a cruise phase or storage mode and (b) in a real time mode. During the real time mode, observations at high spatial (octosectoring) and temporal (0.5s) resolution in the cometary environment permit studies to be made of accelerated particles at the bow shock and/or in the tail of the comet. In conjunction with magnetic field measurements on board Giotto, observations of energetic electrons and their anisotropies can determine whether the magnetic field lines in the cometary tail are open or closed. Further, the absorption of low energy solar particles in the cometary atmosphere can be measured and such data would provide an integral value of the pertaining gas and dust distribution. Solar particle background measurements during encounter may also be used to correct the measurements of other spacecraft borne instruments potentially vulnerable to such radiation.

Solar particle flux measurements, obtained during the cruise phase will, when combined with simultaneous observations made by other spacecraft at different heliographic longitudes, provide information concerning solar particle propagation in the corona and in interplanetary space.     

Advanced pointing systems for space astronomy

Requirements on image stability are increasing, often at the same time that instrument external disturbances are increasing. Pointing large diameter optics from the shuttle bay is the prime current example of this situation. In order to achieve cost-effective advanced pointing systems in the face of these problems, a system approach must be taken that encompasses a realistic assessment of requirements, the best possible detector technology, and a broad look at space vehicles and pointing systems that are available. As an example, a rocket instrument for making measurements of the interstellar gas uses a standard pointing system to achieve a spectral resolution of 2 × 10⁵.     

Satellite measurements of atmospheric composition

Since 1978 a number of satellite borne sensors have been used to measure the composition of the earth's atmosphere. These include the LIMS and SAMS instruments on the Nimbus 7 satellite (launched in October 1978), the SAGE instrument on the AEM2 satellite (launched in february 1979) and various instruments on the SME spacecraft (launched October 1981). For many species, these have provided the first abundance measurements with high spatial and temporal resolution and with global coverage. In this paper the composition measurements that have become available from these programs will be reviewed. The paper will then describe some recent studies that have made use of the new data. As it is the exclusive subject of another invited paper, ozone will not be discussed in in any detail.     

The ROSAT mission

A primary scientific objective of the ROSAT mission is to perform the first all-sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. A large number of new sources (? 10⁵) will be discovered and located with an accuracy of 1 arcmin or better. These will comprise almost all astronomical objects from nearby normal stars to distant quasistellar objects. After completion of the survey which will take half a year the instrument will be used for detailed observations of selected sources with respect to spatial structure, spectra and time variability. In this mode which will be open for guest observers ROSAT will provide substantial improvement over the imaging instruments of the Einstein observatory.The main ROSAT telescope consists of a fourfold nested mirror system with 83 cm aperture having three focal plane instruments. Two of them will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 2°, an angular resolution of ≈ 30″ in the pointing mode and a spectral resolution ^ΔE/E ≈ 45% FWHM at 1 keV. The third focal instrument will be a high resolution imager (≈ 3″). The main ROSAT telescope will be complemented by a parallel looking Wide Field camera which extend the spectral coverage into the XUV band.     

Instrumentation and data systems for high-time resolution study of space plasma shocks

This paper deals with the principal methods of achieving high-time resolution measurements for the study of fine structure of shocks and other discontinuities in space plasmas. In the measurements of ion energy spectra, we have obtained the time resolution about 1s.In the Soviet-Czechoslovak INTERSHOCK project we will obtain temporal resolution better than 0.1s in the measurement of the main plasma parameters. This will be obtained with the multichannel energy spectrometer and the on-board data acquisition and processing system triggered by the shock signature. This system controls the data sampling rate from some scientific instruments and switches on a high-sampling rate near the shock. The method implies detecting a shock by means of on-board processing of magnetic field and plasma parameters. The algorithm for this detection uses both parameters separately as well as in combinations.     

Advances in auroral imaging from space

Space imaging of the aurora provides unique quantitative information on the instantaneous global distribution and pattern of the aurora - a direct result of particle acceleration and precipitation processes occurring throughout the magnetosphere. Techniques for imaging from space have usually involved systematically scanning a detector across the earth using some combination of satellite motion and spin, scanning mirrors, and/or electronic scanning. The recent advent of CCD image sensor arrays opens up possibilities for vastly improved sensitivity and resolution in satellite imagers, although scanning systems retain significant advantages in situations where scattered light is a problem and where narrow band optical interference filters are needed.A new type of imaging instrument being built in Canada for the Swedish Viking satellite will employ a two-dimensional CCD array detector which is fibre-optically coupled to a micro-channel plate intensifier. It will produce images of low light level auroral emissions at the rate of one image per spin of the satellite (20 seconds). The instrument operates in the vacuum ultraviolet and uses a fast inverse Cassegrain optical system. Charge is shifted in the CCD imaging array in synchronism with the moving image so that exposure times of approximately one second will be achieved.     

Quality assessment by region in spot images fused by means dual-tree complex wavelet transform

This work is motivated in providing and evaluating a fusion algorithm of remotely sensed images, i.e. the fusion of a high spatial resolution panchromatic image with a multi-spectral image (also known as pansharpening) using the dual-tree complex wavelet transform (DT-CWT), an effective approach for conducting an analytic and oversampled wavelet transform to reduce aliasing, and in turn reduce shift dependence of the wavelet transform. The proposed scheme includes the definition of a model to establish how information will be extracted from the PAN band and how that information will be injected into the MS bands with low spatial resolution. The approach was applied to Spot 5 images where there are bands falling outside PAN’s spectrum. We propose an optional step in the quality evaluation protocol, which is to study the quality of the merger by regions, where each region represents a specific feature of the image. The results show that DT-CWT based approach offers good spatial quality while retaining the spectral information of original images, case SPOT 5. The additional step facilitates the identification of the most affected regions by the fusion process.     

Using the MIR bands in vegetation indices for the estimation of grassland biophysical parameters from satellite remote sensing in the Alps region of Trentino (Italy)

Development of new methods for estimating biophysical parameters can be considered one of the most important targets for the improvement of grassland parameters estimation at full canopy cover. In fact, accurate assessment methods of biophysical characteristics of vegetation are needed in order to avoid the uncertainties of carbon terrestrial sinks.

Remote sensing is a valid tool for scaling up ecosystem measurements towards landscape levels serving a wide range of applications, many of them being related to carbon-cycle models. The aim of this study was to test the suitability of satellite platform sensors in estimating grassland biophysical parameters such as LAI, biomass, phytomass, and Green herbage ratio (GR). Also, we wanted to compare some of the most common NIR and red/green-based vegetation indices with ones that also make use of the MIR band, in relation to their ability to predict grassland biophysical parameters.

Ground-truth measurements were taken on July 2003 and 2004 on the Monte Bondone plateau (Italian Alps, Trento district) in grasslands varying in land use and management intensities. From satellite platforms, an IRS-1C-LISS III image (18/07/2003; 25 m resolution in the visible-NIR and 70 m resolution in the MIR) and a SPOT 5 image (27/07/2004, 10 m resolution in the visible-NIR and MIR) were used.

LAI, biomass, and phytomass measurements showed logarithmic relationships with the investigated NIR and red/green-based indices. GreenNDVI showed the highest R² values (0.59, IRS 2003; 0.60, SPOT 2004). Index saturation occurred above approximately 100–150 g m⁻² of biomass (LAI 1.5–2). On the other hand, GR relationships were shown to be linear. MIR-based indices performed better than NIR and red/green-based ones in estimating biophysical variables, with no saturation effect. Biomass showed a linear regression with Canopy Index (MIR/green ratio) and with the Normalised Canopy Index (NCI) calculated as a normalised difference between MIR and green bands (IRS: R² = 0.91 and 0.90, respectively. SPOT: R² = 0.63 and 0.64). Similar correlations could also be found for LAI and phytomass, and GR predictability was shown to be higher than NDVI and GreenNDVI. According to these results obtained in the investigated areas, phytomass, biomass, LAI, and GR are linearly correlated with the investigated MIR band indices and as a result, these parameters could be estimated from the adopted satellite platforms with limited saturation problems.     

Integration and calibration of a multi slit spectropolarimeter

Multi-slit spectropolarimeter is a next-generation spectropolarimeter to obtain vector magnetic field information at high spatial, spectral, and temporal resolution for studying the magnetic structures on the Sun. Once developed, it can be used as ground based instrument at solar observatories, also as a space payload for various solar missions. A high spectral resolution is invariably an important parameter for accurate vector magnetic field measurements and faster cadence is required for the study of dynamical evolution of structures (e.g., solar flares, sunspots etc.) on the Sun and hence better understanding on the physics behind their evolution.     

Comparison of solar soft X-ray irradiance from broadband photometers to a high spectral resolution rocket observation

The solar soft X-ray (XUV; 1–30 nm) radiation is highly variable on all time scales and strongly affects the ionosphere and upper atmosphere of Earth, Mars, as well as the atmospheres and surfaces of other planets and moons in the solar system; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. While there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the lack of high spectral resolution measurements in this wavelength range. The conversion of the XUV photometer signal into irradiance requires the use of a solar spectral model, but there has not been direct validation of these spectral models for the XUV range. For example, the irradiance algorithm for the XUV Photometer System (XPS) measurements uses multiple CHIANTI spectral models, but validation has been limited to other solar broadband measurements or with comparisons of the atmospheric response to solar variations. A new rocket observation of the solar XUV irradiance with 0.1 nm resolution above 6 nm was obtained on 14 April 2008, and these new results provide a first direct validation of the spectral models used in the XPS data processing. The rocket observation indicates very large differences for the spectral model for many individual emission features, but the differences are significantly smaller at lower resolution, as expected since the spectral models are scaled to match the broadband measurements. While this rocket measurement can help improve a spectral model for quiet Sun conditions, many additional measurements over a wide range of solar activity are needed to fully address the spectral model variations. Such measurements are planned with a similar instrument included on NASA’s Solar Dynamics Observatory (SDO), whose launch is expected in 2009.     

Development of autonomous control in a closed microbial bioreactor.

Space-based life support systems which include ecological components will rely on sophisticated hardware and software to monitor and control key system parameters. Autonomous closed artificial ecosystems are useful for research in numerous fields. We are developing a bioreactor designed to study both microbe-environment interactions and autonomous control systems. Currently we are investigating N-cycling and N-mass balance in closed microbial systems. The design features of the system involve real-time monitoring of physical parameters (e.g. temperature, light), growth solution composition (e.g. pH, NOx, CO2), cell density and the status of important hardware components. Control of key system parameters is achieved by incorporation of artificial intelligence software tools that permit autonomous decision-making by the instrument. These developments provide a valuable research tool for terrestrial microbial ecology, as well as a testbed for implementation of artificial intelligence concepts. Autonomous instrumentation will be necessary for robust operation of space-based life support systems, and for use on robotic spacecraft. Sample data acquired from the system, important features of software components, and potential applications for terrestrial and space research will be presented.     

敏捷数字电离层测高仪系统研制及初步观测

在小型天线和低发射功率条件下，保证电离层测高仪观测数据质量和提高观测速度一直是电离层垂测的技术难点.针对这一问题，基于新近发展的高速数字芯片和射频器件，采用窄带跟踪滤波、脉冲压缩、编码复用和天线均衡匹配等技术，设计和研制一种敏捷数字电离层测高仪.该系统采用数米高的小型收发天线和便携式主机系统，配置任意频率扫描方式频高图、高分辨率多普勒频高图和斜向探测等多种工作模式，具有可流动观测布站、系统参数灵活捷变及适合快速电离层扰动探测等能力.敏捷数字电离层测高仪为组网观测获得大范围电离层时空变化和电离层快速扰动及传播提供了一种有效的探测手段.      

Recent developments in space-borne zodiacal light photometry

The 1985 International Solar Polar Mission will provide the first opportunity to perform measurements from out of the ecliptic and from above the solar poles. Included in this mission is the Zodiacal Light/Background Starlight Experiment of the Ruhr-University Bochum, FRG (in collaboration with the State University of New York at Albany). The experiment is based on the use of a multicolor, sky-scanning photopolarimeter, which will be carried on the NASA S/C.The scientific objectives of the experiment are to investigate the intensity, polarization, and color of the diffuse sky brightness and determine the spatial distribution and physical properties of the interplanetary dust, including a possible interstellar component, as a function of S/C position in and out of the ecliptic.The instrument will allow simultaneous measurements in two separate wavelength bands. Measurements will be performed at 180, 220, 240, 280, 320, 350, 360, 440, 540, 640, 800 nm, including the state of polarization. Two different fields-of-view (1 sq deg and 5.6 sq deg) can be selected.The use of a microprocessor system in the instrument electronics will provide flexibility in measurement sequences and programs, on-board data processing and data quality control.     

Studies of optical and biological properties of landcover employing shuttle flights of a multispectral linear array radiometer

Studies to characterize optical and biological properties of land cover as observed from space are planned using a six channel, imaging spectroradiometer employing newly developed multispectral linear array (MLA) detector technology. These studies are to take place by mounting the radiometer on the Shuttle and observing areas with dynamic and diverse types of land cover condition. The radiometer will have 15 meter spatial resolution for four, 20 nanometer bands in the visible and near infrared and 30 meter resolution for similarily narrow bands in the shortwave infrared bands. The instrument will scan ± 45 degrees along the Shuttle orbital path. The principle objective of this experiment is to obtain observations that augment knowledge of the distribution of basic land cover types in regions that are known to be key to questions of biogeochemical cycles, energy balance and climatic change. Another key objective is to quantify the bidirectional reflectance of key land cover conditions in major portions of the visible, near infrared and shortwave infrared as they are observed from space. The initial execution of this experiment is presently scheduled for late 1987.     

Space telescope studies of Jupiter and Saturn simulated by Voyager observations

Space Telescope (ST) observations of Jupiter and Saturn will offer a unique opportunity for monitoring their changing meteorological characteristics. They will provide higher spatial and temporal resolution for composition and vertical structure studies than have been available to date. We have simulated the planetary camera observations of Jupiter and Saturn by Voyager images of the appropriate spatial scale. With this data set we have investigated the meteorological properties of these atmospheres which can be studied at these scales. In addition we have considered the advances obtainable with the high resolution spectrometer on ST compared with observations from ground-based and other Earth-orbiting satellites. These studies will provide insight into the scientific gain and possible problems in the use of ST for planetary studies.     

Derniers resultats de calcul d'orbite SPOT et TOPEX/POSEIDON obtenus avec DORIS

DORIS is a tracking system developed by CNES to support precise orbit computation of the US-French TOPEX/POSEIDON project. Moreover DORIS data are currently processed to compute SPOT2 and SPOT3 orbits. Although the SPOT satellites are at 800 km altitudes, their orbits reach the decimetric level, to be compared to the 3–4 cm RMS on the T/P radial component.For each type of orbit, there is an adaptive period of a few months which is used for improving the precision. The paper describes what has been done to reduce some items in the total error budget. The latest results will be presented as well as the criteria which are settled to characterize the improvements.Finally, the future developments of DORIS and the potential projects flowing DORIS will be outlined such as ENVISAT and TOPEX/POSEIDON Follow On.     

InfraRed Astronomy Satellite Swarm Interferometry (IRASSI): Overview and study results

The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO) and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of five satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1–6 THz. Precise knowledge on the baselines will be ensured by metrology methods employing laser-based optical frequency combs, for which preliminary ground-based tests have been designed by members of our study team. We first give a motivation on how the science requirements translate into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, in quasi-real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals and will ultimately affect the accuracy of the baseline estimations.     

Utilization of spot for mineral exploration,with special reference to Western Africa

The first SPOT 1 images show that data quality is in fairly good agreement with the SPOT simulations on which the geological community has worked in recent years. SPOT data are particularly useful in mineral exploration for the following reasons :- ground resolution (10 m and 20 m) proves to be very effective at scales such as 1/50,000. It considerably improves the identification of secondary structural features that may be significant for mineral exploration- stereoscopy makes it possible to quantify the dip of bedding, thickness of layers, fault displacement, etc.- acquisition flexibility is an additional advantage in the case of programs requiring multitemporal data.Two examples from Western Africa are described :- Poura, Burkina Faso : gold mining prospect- Bandiagara, Mali : reconnaissance study.SPOT makes it possible to bridge the gap between the regional information provided by Landsat data and that provided by ground of large scale aerial photographic surveys, with the advantage of multispectral images.     

Study of the optical and mechanical properties of regolith with the ICAPS facility

Regoliths are a most important component of solar system bodies. The study of their formation and evolution depends upon measurements from orbiting spacecraft or Earth-based observations, and by the development of models addressing formation and evolution scenarios, physical properties and composition of the constituent materials. For asteroids and comets, recent measurements tend to confirm the idea of extremely low bulk densities. The porosity of the outermost regolith layers should thus reach very high values. Regolith formation and growth partly depends upon gravity and mechanical properties of its constituent particles, which are very poorly documented. Gravitational effects play an important role in the shaping processes of large bodies, while material strength properties are more important for smaller bodies. The understanding of both, aggregation processes of, and of light scattering from, such media, would strongly benefit from experiments led under microgravity, and provide insight into regolith formation processes: much lower collision and aggregation velocities can be achieved in a microgravity environment, leading to the formation of much fluffier aggregates than possible on Earth. ICAPS is a multi-year scientific programme to simulate cosmic and atmospheric particle systems on board the International Space Station. The ICAPS facility will allow to build simulated regolith and thus enable the study of their mechanical and optical properties. Measurements such as tensile strength, electrical and thermal conductivities, compressibility and porosity, will be made, as well as monitoring of collisions into such simulated regolith. The article discusses the ICAPS research plan for regolith studies and the facility current status.