Active remote sensing

There are two categories of remote sensing, active and passive. Passive techniques utilise electromagnetic radiation emitted from or transmitted through the atmosphere, the radiation source being for example the black body emission from the earth s surface or solar and stellar irradiances. The most critical part of a passive remote sensing instrument is its detector. In contrast, active remote sensing systems have their own radiation source and a detector, for example, radar and lidar techniques. 

In Fig.6.71 different passive and active remote-sensing techniques are illustrated. The selective reflection of solar radiation from the earth s surface, the absorption or the thermal emission of the atmosphere can be studied with passive techniques. Active techniques frequently make use of laser or microwave radiation. The transmission or scattering of such radiation can yield information on the atmosphere or the land and sea surface. 

We will discuss two active remote-sensing techniques for the atmosphere — the long-path absorption technique and the lidar technique. However, we will first consider a passive technique, in which lasers play an important part in the detection scheme. This optical heterodyne technique is even more frequently used for signal recovery in connection with the active optical remote-sensing methods. The field of laser monitoring of the atmosphere is covered in several monographs and articles [10.70-10.76]. 

The SPATE 9000, used in the experimental activity, is a remote sensing system able to detect... 

Hereia optical spectroscopy for laboratory analysis, giving some attention to remote sensing usiag either active laser-based systems (13—16) or passive (radiometric) techniques (17—20), is emphasized. 

H. Claustre, S.B. Hooker, L. Van Heukelem, J.-F. Berthon, R. Barlow, J. Ras, H. Sessions, C. Targa, C.S. Thomas, D. van der Linde and J.-C. Marty, An intercomparison of HPLC phytoplankton pigment methods using in situ samples application to remote sensing and database activities. Marine Chem. 85 (2004) 41-61. 

DeRossi, G. Puccetti, G. and Puccini, M. (1994) Airborne Polar experiment -technical activities for the integration on M55 Myashischev aircraft of a scientific instruments payload, Proceedings of the First International Airborne Remote Sensing Conference and Exhibition, Strasbourg, France. 

In the last 23 years remote sensing of atmospheric constituents has established itself as an important research field. Global remote sensing observations are essential to understand the natural processes which determine the global behaviour of the atmosphere and to assess the impact of human activity on the atmosphere. In addition, remote sensing of the atmosphere provides data needed to assess die impact of international agreements designed to limit the environmental impact of industrial activity. 

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. 

The analysis of spatio-temporal variations of phytoplankton biomass in the Black Sea was based on the remotely sensed data collected by the SeaWiFS (September 1997-May 2006) and MODIS-A (July 2002-May 2006) satellite sensors. The data were obtained from National Aeronautics and Space Administration Goddard Space Flight Center Distributed Active Archive Center (NASA GSFC DAAC) [6]. We used monthly averaged Level 3 standard mapped... 

In recent years, in order to study the features of phytoplankton development, satellite observations have been actively applied (see chapter Seasonal and inter annual variability of remotely sensed chlorophyll in this volume). The use of satellite data allows one to actually observe the spatial changes in phytoplankton on scales from tens to hundreds of kilometers that occur... 

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