7 elements of remote sensing process Energy Source (A) Radiation & Atmosphere (B) Interaction with Targets (C) Recording of Energy by Sensor (D) Transmission & Reception (E) Interpretation and Analysis (F) Application (G)

Extract meaningful information from imagery 6. Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally, to extract information about the target which was illuminated.

4.3 Digital Image Processing Common image processing image analysis functions: A. Preprocessing B. Image Enhancement C. Image Transformation D. Image Classification and Analysis

Background DIP - manipulation & interpretation of images Began in 1960’s 1972 - Landsat 1 launched Access to low cost, efficient computers Access to imagery

Pixel Digital spatial image - made up of a grid of cells, each containing a value or measurement and representing an area of the Earth’s surface.

Digital Number (DN) - value stored within a pixel of an image, represents amount of light reflected back to sensor. digital format – images are represented in a computer as arrays of pixels.

Multispectral images - multiple layers representing different parts of the EMS.

1. Pre-Processing (Image Rectification) Initial processing of raw data prior for analysis Correct for distortion due to characteristics of imaging system & imaging conditions.

2. Image Enhancement Solely to improve appearance of imagery. Increasing visual distinction Un-enhanced images usually appear very dark - little contrast - difficult to visually interpret. Various procedures applied to image data in order to more effectively display data for visual interpretation.

Computers - ideal for manipulating and analyzing large continuous data sets displayed as grayscale. Used to distinguish between slight spectral variations and enhance them.

Lanier.img (4-3-2) Swipe

Applying a histogram stretch produces a simple classification of urban, agricultural, and mixed use areas.

A. Contrast stretching Linear grey-level stretching Lower threshold value is chosen so that all pixel values below threshold are mapped to zero. Upper threshold value is chosen so that all pixel values above threshold are mapped to 255. All other pixel values are linearly interpolated to lie between 0 and 255. Lower and upper thresholds are usually chosen to be values close to the minimum and maximum pixel values of the image.

0 = black 255 = white

A sensor measures the electromagnetic energy within its range. Total intensity of the energy from zero to the maximum is broken down into 256 brightness values for 8-bit data.

Two types of histogram stretches