Carlo Ulivieri

A split window algorithm for estimating land surface temperature from satellites

Abstract The use of multichannel approaches has led to significant improvements in the accuracy of remotely sensed surface temperature determination. Nevertheless, even if with different targets from land versus ocean applications, some tasks have required further investigations. In this work a genera; multichannel algorithm, taking separately into account atmospheric water vapour, surface emittance and air-surface temperature difference, is described; thus, it results an extension of the split-window algorithm and is able to give a land surface temperature assessment by means of a formalism valid for a wide range of atmospheric water vapor and surface emittance. The surface-emittance effect has been analyzed in detail, making a comparison with other proposed algorithms; namely the knowledge of surface emissivity and its variation with wavelength has been considered. The algorithm has been set up by accurate simulations of NOAA satellite measurements. An analysis has been also carried out in order to study the feasibility of a remote sensing mission for detecting land surface temperatures for mid latitude regions.

satellite de-orbiting by means of electrodynamic tethers part i: general concepts and requirements

Abstract It has been recently suggested that conductive tethers, besides other applications, may be effective for the de-orbiting of satellites at the end of their operational life. In this paper we give a preliminary evaluation of this capability with respect to a well-defined tether system and using the expertise and results from the recently flown TSS-1 project. The system considered is a long conducting tether, covered by an insulator, with a passive electron collector at the positive termination and a hollow-cathode electron emitter at the opposite end. In analyzing this system, we point out the crucial importance of the contact impedances associated to the coupling between the tether terminations and the ionospheric plasma. We give a first evaluation of the de-orbiting time for a typical case and conclude about feasibility of a tether system to de-orbit satellites.

Land Surface Temperature Retrievals from Satellite Measurements

Abstract This paper discusses the importance of considering both atmospheric absorption and surface emittance in an accurate assessment of land surface temperature. This is obtained by combining the measurements in two spectrally close radiometric channels of NOAA-AVHRR/2 instruments (Split Window Channels), accurately simulated for different atmospheric and terrestrial conditions. The approach, that usually takes into account the atmospheric effects, has been improved, with the addition of a term depending only upon surface emittance. The proposed algorithm, that provides an estimate of land surface temperature within ±1°C if spectral surface emittance is known, has been applied to AVHRR/2 data to obtain surface temperature maps of the Northern Italy.

SATELLITE DE-ORBITING BY MEANS OF ELECTRODYNAMIC TETHERS PART II: SYSTEM CONFIGURATION AND PERFORMANCE☆

Abstract This paper aims to assess the efficiency of a de-orbiting system based upon conductive tethers under realistic assumptions for its interaction with the ionospheric environment. We analyze the configuration made up of a 2.5– 10 km tether, a passive inflatable collector of 2.5– 10 m radius at the positive termination and a hollow cathode at the negative one. Voltages and current in the system are computed from the equation of the equivalent circuit, making use of the IRI-90 ionospheric model. The resulting electromagnetic drag forces have been used to compute the evolution of the orbital elements (especially the semi-major axis) and the re-entry times. Our results indicate that a typical satellite of 500 kg mass at 1300 km altitude can de-orbit in 20–100 days, for a broad range of orbital inclinations and solar activity. The validity of the concept is further strengthened by the comparison with alternative propulsion systems.

Long-term effects on lunar orbiter

Abstract The motion of lunar satellites has been intensively studied in the past by interesting semi-analytical methods. However, the poor knowledge of the Moons gravity field makes those results incomplete. Subsequent lunar missions have allowed a more precise determination of the lunar gravity coefficients. Moreover, renewed scientific interest in the Moon has generated several more accurate models for the motion of a lunar orbiter. It is known that many zonal harmonic coefficients of the Moon have the same order of J 2 and must be included in a first-order perturbative theory. Despite of this, some success has been achieved in the study of long-term evolution of a lunar orbiter. In particular, “frozen” orbits have been found, that is orbits whose parameters have almost vanishing long period evolution. That is, these orbits can be regarded as equilibrium configurations of the orbital dynamics, and they are of interest for the general understanding of the free motion of an orbiter as well as reference orbits, taken in order to minimize the costs of a controlled spacecraft. However, stability of these equilibria has also to be checked with respect to other perturbations of the same order, such as the effects due to the Earth and, to a lesser degree, due to the Sun. We show that these perturbations, together with the effects induced by the lunar orbital plane motion, are rather relevant. We develop a picture analogous to the geometric approach to the motion of an Earth satellite under the influence of three poles ( J 2 , Moon and Sun). The presence of more poles of perturbations (due to the other harmonics) makes the picture more complex but similar. Interesting effects on the frozen orbits as well as on the general motion of the pole and eccentricity of a lunar orbiter are found.

Remote Sensing and GIS Techniques for Natural Disaster Monitoring

On 26 Dec 2004, a magnitude 9.0 earthquake occurred off the west coast of northern Sumatra, Indonesia. Over 300,000 people lost their lives in this disaster. Areas near to the epicentre in Indonesia, especially Aceh, were devastated by the earthquake and tsunamis.

A small satellite constellation for continuous coverage of mid-low earth latitudes

When located on a geostationary orbit, a satellite keeps a steady position with respect to a generic point on the Earth’s surface and this characteristic allows for important advantages. A continuous longitudinal coverage of the Earth’s surface (higher latitudes excluded) is a result of using a three geo-satellite constellation. Nevertheless, there are also several drawbacks related to the geostationary orbit employment. The need to consider alternative satellite constellations has begun to arise from these disadvantages; these constellations, in spite of having very similar characteristics to the geostationary system, are able to overcome the complexity, the costs and the launching site problems connected with a geostationary satellite. For equatorial orbits, the Four-Leaf Clover System represents a profitable alternative compared to the traditional geostationary system. As far as high Earth latitudes are concerned, there are different operational constellations, such as Molniya and Tundra, capable of ensuring the continuous coverage of a region and generally taking orbits with a critical inclination into account (63.43 deg). The aim of this paper is to demonstrate that it is possible to create a satellite constellation capable of ensuring a continuous coverage of mid-low Earth latitudes. After a general study of the orbits employed to date, followed by a general graphical representation, a constellation of eight small satellites in multi-synchronous orbits makes the achievement of this paper’s aim possible. Several possibilities for application follow, both for telecommunications and remote sensing missions.

Derivation of land surface temperatures from MODIS data using the general split‐window technique

Fast Atmospheric Signature Code (FASCODE), a line‐by‐line radiative transfer programme, was used to simulate Moderate Resolution Imaging Spectroradiometer (MODIS) data at wavelengths 11.03 and 12.02 µm to ascertain how accurately the land surface temperature (LST) can be inferred, by the split‐window technique (SWT), for a wide range of atmospheric and terrestrial conditions. The approach starts from the Ulivieri algorithm, originally applied to Advanced Very High Resolution Radiometer (AVHRR) channels 4 and 5. This algorithm proved to be very accurate compared to several others and takes into account the atmospheric effects, in particular the water vapour column (WVC) amount and a non‐unitary surface emissivity. Extended simulations allowed the determination of new coefficients of this algorithm appropriate to MODIS bands 31 and 32, using different atmospheric conditions. The algorithm was also improved by removing some of the hypothesis on which its original expression was based. This led to the addition of a new corrective term that took into account the interdependence between water vapour and non‐unitary emissivity values and their effects on the retrieved surface temperature. The LST products were validated within 1 K with in situ LSTs in 11 cases.

A new perspective on oil slick detection from space by NOAA satellites

In this paper an extension of the Split Window Technique algorithm, to account for small surface emissivity variations, is presented. This algorithm has been used, along with an adaptive filtering pattern recognition approach, in order to detect oil spills on the sea surface under the assumptions of thermal equilibrium between the oil polluted areas and the surrounding water, of weak horizontal sea surface temperature gradients (i.e., <1°C) in the area of interest and of a horizontal uniform atmospheric water vapour distribution over the discharged area. AVHRR/2 data acquired both on the Gulf of Genoa in April 1991 during an oil pollution episode following the wreck of the Haven tanker and on the Persian Gulf during war operations in January-February 1991 were considered. Comparing satellite retrieved polluted areas with in situ observations available in literature and high spatial resolution satellite observations (Landsat and SPOT), the algorithm has proved to supply satisfactory results in detecting oil contaminated areas.

On radiative and conductive heat transfer in spacecraft

Abstract The “radiative” boundary condition in a heat conduction problem relates the heat flux in a point of the wall to the temperatures in all the other points of the surface system. That is, this condition is of a “functional” type. This “functional” can be solved in discrete terms by using the conventional technique of dividing the body in small discrete elements or “nodes”. This paper instead presents an approach on a continuous scheme, by which the functional is solved in terms of “spacewise harmonics” of the temperature inside the body; the heat conduction problem is thus reduced to an ordinary form differential system whose unknowns are these “harmonics”. An interative linearized procedure to solve this system is also suggested, by which “exact” solutions are obtained. The merits of these solutions, with respect to practical discrete element computations, are in the better spacewise resolution and in the consequent more accurate treatment of both radiation and conduction. The application of the procedure is, however, limited to particular geometries. It is relevant to note that among these possible geometries many are included of practical interest, like hollow cylinders and polygons, cubic boxes etc. A numerical example completes the work.