Image Interpretation: Types Of Data Products

TYPES OF DATA PRODUCTS

The main interest of social scientists and applied scientists is the data produced by Remote Sensing technique. The Remote Sensing data are of two types - pictorial and digital. These data products are described in the following paragraphs:

1 DIGITAL DATA PRODUCTS:

The digital data products give information in the form of array of small cells having quantitative values which is the function of the electromagnetic energy radiated from all objects within the field of view. A digital data product is called digital image. A digital

image is a two dimensional array of pixels (picture elements). Each pixel represents an area on the earth's surface and has an intensity value (represented by a digital number) and a

location address (referenced by its row and column number). The intensity value represents the measured solar radiance in a given wavelength band reflected from the ground. The location address is a one-to-one correspondence between the column-row address of a pixel and the geographical coordinates (e.g. latitude and longitude) of the imaged location. The digital image is a vast matrix of numbers and is very often stored in amagnetic tape and in particular in a computer compatible tapes (CCT). The digital data can be converted into photographic image.

2 PICTORIAL DATA PRODUCTS

The pictorial data products give information of objects on the earth surface in the form of photographs or images. The pictorial products provided by aircrafts are called aerial photographs. These are generally taken by sophisticated cameras which use visible portion of electromagnetic energy. Therefore, aerial photographs give the exact view / picture of objects on the earth surface on reduced scale. The aerial photographs may be black and white or may be coloured, it depends upon the camera used in aircraft. The pictorial data products provided by satellites are called satellite images. These images are generally taken by sensors which use both visible and invisible portion of electromagnetic energy. The satellite images can be black and white or can be coloured. The black and white pictures or images are produced from each band of digital data. For a particular band, black and white image is generated by assigning different shades of grey (white to black) to its digital data. Likewise unicolour images (blue, green, red etc.) can be generated by assigning different shades of blue / green/ red to a particular band data. When any three bands are combined, it gives multi coloured imagery. If images are taken in blue, green and red bands (visible portion of electromagnetic energy) respectively, they can be combined to give natural colour image. If images are taken in green, red (visible portion of electromagnetic energy) and infrared band (invisible portion of electromagnetic energy) and   blue,   green and   red colours  are  assigned  to  them respectively  and then  they are combined together, it will produce a False Colour Composite (FCC) image. The FCC image does not give the exact picture / view of the earth's surface like aerial photographs. The lay person cannot visualize anything from FCC image. Only an expert can interpret it.