Radar concepts, as understood by radR

The images below describe radR's data and statistical models:

• radR data model
  
• stats model
• stats model related to the blip parameters window
  

Note: this is not a summary of standard radar theory, but rather a description of the conceptual model radR uses to process radar data.

A rotating antenna sends out electromagnetic pulses and listens for an echo.  The antenna angle is between the horizontal plane and the structural (not rotational) axis of the the antenna.  The antenna aperture is the geometry of the region from which the antenna can detect an echo from a single pulse.  When this region is approximately cone-shaped and centred on the structural axis, the aperture can be defined by a single aperture angle.

The strength of the echo over time is digitzed into a sequence of samples.  A sample value is represented as an integer with d bits per sample, giving a sample range of 0 ... 2 ^ d - 1. Typically, d is 8 or 12, giving a sample range of 0 ... 255 or 0 ... 4095.

A scan is the matrix of sample data from one rotation of the antenna.  Sometimes this matrix is referred to as raw data, to distinguish it from scan converted data (see below).

A scan row (of a scan matrix) is the set of N consecutive samples from the echos of one pulse. Scan conversion is the process of building a pixel matrix, a two-dimensional spatial representation of the scan matrix.   Each pixel in the matrix represents one or more samples.  A pixel's classis the class of the sample at the centre of the pixel.  A pixel's value is the average value of the sample(s) represented by the pixel. A pixel represents the sample at its centre, as well as up to 2 angular and 2 radial neighbour samples, depending on the zoom level (see below) and the location of the pixel relative to the plot centre (see below).

The screen colour of a pixel is selected according to its value from the palette for its class.

The plot window is the rectangular region of pixels which are actually displayed on the screen. The plot centre is the location of the imaginary pixel where samples of index 0 would be displayed.  The plot centre need not be within the plot window, which allows for panning the window across the scan disk.

The zoom level is the width in pixels of those samples which are plotted parallel to the screen's horizontal axis. For example, if the zoom level is 3, then a sample from a pulse that is due east or due west will be drawn 3 pixels wide.  The same scale applies to the vertical axis.  Fractional zoom levels are allowed.

In radR, because scan conversion is purely for visualization, it is only performed for pixels visible in the plot window.  In contrast, computations for finding and filtering blips always use the full raw scan matrix.