5.RECONNAISSANCE SURVEY - METHODOLOGICAL APPROACH

 

Considering the land to survey is a virgin one then reconnaissance survey is very helpful to locate the effective area with maximum probability of  fresh groundwater. The reconnaissance survey is particularly suitable to the assessment of land resources over a large area. It is based on a holistic approach , according to which the main components of the land such as soil, vegetation, geomorphology, hydrology are not considered individually, but as a whole. They are mapped simultaneously, taking also into account interactions between them and the man's influence, so that the earth's surface is the result of something more than just the sum of all its components.

 

The weight of image processing and interpretation, compared to the weight of the field work, increases as the scale of the survey decreases, reaching its maximum at smaller scales, such as exploratory and reconnaissance surveys.

                     

                                   Figure 1 - Flow chart of the whole methodology.

 

 

Image Processing

 Satellite images are used for the preliminary interpretation of the area under study. In selecting the images care is taken, besides the cloud cover, of the acquisition period, for instance, early springtime images are particularly suitable in detecting the vegetation status and the crops as they shows the best combination between the low inclination of solar radiation at soil - which helps the observation of morphological aspects - and plants growth.

 

Preliminary Legend and Visual Image Interpretation

The consultation of available bibliographic material allows to define the preliminary interpretation keys of satellite images which are analysed by a team of specialists, in order to produce a preliminary map of areas showing internal homogeneous spectral properties.
Interpretation of the above satellite image:

sparse desert vegetation, reddish soils, and stone darkened by an inorganic patina of oxidization. Construction land appears brighter. Bulldozed soil, bare of vegetation, is very reflective.

A young neighborhood appears medium green (medium green) again, perhaps a bit brighter from all the reflective pavement and roofs. The trees are small, and some developments now conserve water by landscaping with rock and desert plants rather than grass.

An old neighborhood appears dark, brownish red (dark, brownish red), from the mature trees and more grass. In these false-color images, photosynthesizing vegetation always adds a red tint. Golf courses appear bright red (bright red) because they are the most intense vegetation. New courses tend to be mixed into residential developments while older courses tend to be separate.

Water appears almost black (almost black) because at this angle it scatters little light back to the Landsat sensor. Like golf courses, water is sometimes integrated into residential developments for recreational purposes.

 

Planning of the Field Survey

 

Once the preliminary interpretation is performed, a field work is required in order to both validate the hypothesis made during the previous phase and to gather necessary detailed information for the characterisation of each cartographic unit.

 

Field Survey

 

The project team visits the study area to carry out direct observation and analysis in the planned releves in order to check the visual classification of the satellite image and to update the preliminary map.
Field work is required in order to both validate the hypotheses made during the previous phase and to gather necessary detailed information for the characterisation of each cartographic unit.
The observation points in the field are located according to specific methods.
For each of them the field work consists in the general description of the standing point and in particular geomorphology. Furthermore, vegetation assessment and soil profiles description are carried out.
In order to facilitate the location of the control points by using the GPS in the field, the preliminary map may be overlaid to a satellite image upon which a geographic grid of reference is previously overprinted.

Data base Implementation

Data gathered during the field survey are stored into a data base linked to related spatial data in order to be managed within a Geographical Information System for an integrated analysis of the study-area.

Corrective Image Interpretation

Relying on field data, the original image interpretation and the legend are revised and properly adjusted in order to provide the final Land Unit Map and relevant legend.