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Interpreting basis for ESA SMART-1/AMIE observations of the Moon with experience from Clementine and Lunar Prospector data analysis, laboratory and theoretical modelling lightscatter in dusty surfaces

Objective

The photometric function is controlled by a small-scale structure of lunar soil. Hence, study of the photometric properties can give information about the soil structure with promising applications to geological studies of the Moon. The most interesting and diagnostically promising is the opposition effect, the strong increase of surface brightness, when the phase angle tends to zero. The photometric function is not exactly the same over the whole lunar surface. Its variations are due to varying surface roughness, typical size of lunar soil particles, their optical heterogeneity, and so on. Therefore, the variations themselves bear valuable information about the lunar surface structure. This work supports studies in preparation for the international project of European Space Agency SMART-1. The SMART-1 micro-camera (AMIE) has a 7-degree field of view and three near-infrared spectral bands. AMIE camera will provide a high spatial resolution. Normally AMIE camera will be directed downward, but other imaging geometries are also possible. It opens unique possibilities for advanced study of the photometric properties of the lunar soil. The main goal of the proposal is development of an interpreting basis for SMART-1 observations of the Moon with experience from Clementine and Lunar prospector data analysis, laboratory and theoretical modelling lightscatter in dusty surfaces.

It is in particular planned:
(1) to produce and to study phase-angle-ratio images of selected lunar regions for determination of their surface roughness characteristics;
(2) to study relationships between phase-angle-ratio anomalies and their geological characteristics;
(3) to determine photometric functions for selected sites and their dependence on albedo;
(4) to search for and to list lunar surface anomalies of photometric function parameters and to recommend selected sites for special investigations for SMART-1 and other future missions;
(5) to study relationships between phase function (opposition effect) parameters with composition of the lunar regolith;
(6) to measure phase functions of simulated lunar regoliths with laboratory photometers and to develop theoretical and computer models of the shadow-hiding opposition effect and coherent backscatter enhancement of regolith-like surfaces.

The project will also provide an accurate procedure of photometric calibration for AMIE images. It is essential that such a procedure will be developed before the actual mapping starts to immediately provide the scientific community with reliable data. The project will also result in recommendations on advanced photometric studies of carefully selected sites on the Moon in frame of the mission, including imaging at extremely low phase angles to study the opposition effect. Among key innovative features of the study, using two unique laboratory optical instruments are important. A new laboratory photometer, which is in disposal of the French team, is able to image the field of study, that gives a unique possibility for direct measurement of shaded area in the field of view, and hence to validate the predictions of the models of the shadow-hiding mechanism. An original laboratory photometer, which is in the disposal of the Ukrainian team, is able to measure photometric properties at extremely small phase angles, which is essential for validation of models of the coherent-enhancement mechanism.

Advanced theoretical study accompanied with computer modelling and validated with laboratory measurements of carefully selected and prepared samples of controlled structure will give a background for reliable quantitative interpretation of variation of photometric properties of the lunar soil. These results will be applied to Clementine data, and in future can be used as a base for interpretation of AMIE/SMART-1 observations. Accomplishment of the project will increase the scientific output of the SMART-1 mission. The accurate photometric calibration will make the AMIE images more attractive for planetology community than the Clementine data set. New knowledge about the lunar surface will be obtained from Clementine images and Lunar Prospector data analysis, e.g., variations of the opposition effect will be interpreted in terms of surface structure parameters with further applications to the geologic history of the Moon. Unknown previously areas of unusual photometric properties (e.g., swirl-like formations) can be found on the lunar farside.

The background for quantitative interpretation of photometric data, which will be established in the project, can be used in future for interpretation of astronomical and spacecraft observations of surfaces of other bodies having no atmosphere, namely, asteroids, satellites of Mars and Jovian planets, and Saturn rings. Some applications are also possible for remote sensing of soil on the Earth and Mars. The results of the project will allow the use of the Moon as a photometric standard for calibration of imaging systems in future space missions.

Coordinator

University of Helsinki

Address

Kopernikuksentie 1
00014 Helsinki

Finland

Participants (3)

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Kharkov State University

Ukraine

M.V. Lomonosov Moscow State University

Russia

Paul Sabatier University/CNRS

France

Project information

Grant agreement ID: INTAS-2000-00792

  • Start date

    1 June 2001

  • End date

    31 May 2004

Funded under:

IC-INTAS

Coordinated by:

University of Helsinki

Finland