植被遥感的现状与展望_英文_

Present Status and Perspectives of Remote Sensing

of Vegetation

Juhan Ross

(T artu Obse r va tory,EE2444Tor a vere,T artu,Estonia)

During the recent decades a new discipline of biogeophysics remote sensing of vegetation has been born.T his w as stimulated by the need to describe in more detail the energy and m ass ex chang e betw een the g round surface and atmosphere in the mathemat-i cal models of the global and reg ional climate,by the need to have rapid inform ation about biological productiv ity and yield of the vegetation over the large areas and probably to most extent by m ilitary needs, connected w ith rocket piloting.The rapid develop-ment of remote sensing has based on:

i)The existence of Earth s satellites,originally constructed for military and astronom ical needs.

ii)The availability of the powerful enoug h com-puter technolog y for recording,data processing and analysis.

iii)The possibility to use the radiative transfer theory originally elaborated for astrophysics, atmospheric physics and neutron transport in nuclear reactors.

T he main problem of remote sensing of the veg e-tation might be formulated as follow s:measuring from satellites or airplanes electromagnetic radiation in optical,therm al and microw ave spectral regions reflected from vegetation and the solv ing the inversion problem to obtain information for classification, distribution,functioning and productiv ity of different kinds of vegetation over the w hole Earth surface. Reflected from veg etation electromag netic radiation is determined by the following factors:

i)Conditions of illumination above the veg eta-tion.

ii)The disturbing influence of the atmosphere in propagation of the reflected radiation.

iii)T he properties of the vegetation and soil in scattering of the radiation.

iv)The architecture of the w hole canopy as w ell as individual plants.

There ex ist different fundamental and practical difficulties which limit the solving of the m ain prob-lem.

1)Within a certain type of vegetation the varia-tion of the reflected radiation is great within pix els variations m ay ex ceed variations between pix els.T he main reason of these variations is the semiregular structure and inhomogeneity of vegetation itself. These v ariations are sm aller for cultural vegetation and greater for natural one, e.g.for forests and shrubs.

2)Nonflat relief of the g round surface changing the conditions of illum ination.

3)The existence of the cloud cover in the Earth atmosphere drastically limiting the possible time for remote sensing in optical and thermal spectral reg ions.

4)Lack of detailed enough information about3D distribution of the optical properties of the atmosphere resulting in erroneous atmospheric correction.

5)Different technical errors,connected w ith sensor calibration and stability,w ith reg istration,da-ta processing,etc.

Due to these difficulties the inverse problem having the measuring data of the reflected radiation about some certain type of vegetation to determine the optical and architectural parameters of this vegetation must be m athematically treated as incorrect inverse

第1卷增刊1997年 5月

遥 感 学 报

JOURNAL OF REM OTE SENSING

V ol.1,Suppl.

M ay, 1997