Data Analysis for Digital Satellite Imagery: Band Interleaved by Pixel Format, Band Interleaved by Line Format (BIL) , and Band Sequential Format (Especially for GATE-Geospatial 2022)

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Remotely sensed data is analysed using various image processing techniques and methods. These include either visual (or analogue) processing techniques applied to hard copy data such as photographs or printouts and the application of digital image processing algorithms to the digital data. One of the purposes of applying both analogue and digital techniques to remotely sensed data is to enable the analyst to see the data in several ways. This process, often termed scientific visualization, can be likened to an individual who finds an object but is unsure of its purpose or origin. He or she may turn it over and over in their hands, feeling the texture of each part of the object and examining the variations in colour on each surface. They may look for clues to its origin in the area surrounding the location the object were found. Some individuals might then proceed to take the object apart and examine the individual components and how they relate one to another. If this individual takes all these steps, they will be intimately familiar with the object they have found. That is the goal of image processing - to allow the researcher to examine their data from all possible angles, to place entire images in context with their surroundings, and to allow the relationships of individual scene elements to be discovered. Scientific visualization is this process of exploring data visually to gain an intimate knowledge of it and, hopefully, insight into it.

Data Formats for Digital Satellite Imagery

Digital data from the various satellite systems supplied to the user in the form of computer readable tapes or CD-ROM. As no worldwide standard for the storage and transfer of remotely sensed data has been agreed upon, though the CEOS (Committee on Earth Observation Satellites) format is becoming accepted as the standard. Digital remote sensing data are often organised using one of the three common formats used to organise image data. For an instance an image consisting of four spectral channels, which can be visualised as four superimposed images, with corresponding pixels in one band registering exactly to those in the other bands. These common formats are:

  • Band Interleaved by Pixel (BIP)
  • Band Interleaved by Line (BIL)
  • Band Sequential (BQ)

Band Interleaved by Pixel Format (BIP)

One of the earliest digital formats used for satellite data is band interleaved by pixel (BIP) format. This format treats pixels as the separate storage unit. Brightness values for each pixel are stored one after another. It is practical to use if all bands in an image are to be used below figure shows the logic of how the data is recorded to the computer tape in sequential values for a four-band image in BIP format.

Band Interleaved by Pixel Format

All four bands are written to the tape before values for the next pixel are represented. Any given pixel located on the tape contains values for all four bands written directly in sequence. This format may be awkward to use if only certain bands of the imagery are needed. Often data in BIP format is organized into four separate panels, or tiles, consisting of vertical strips each 840 lines wide in the x-direction and 2,342 lines long in the y-direction. In order to read all four bands of the image, all four panels must be pieced together to form the entire scene (Campbell, 1987) .

Band Interleaved by Line Format (BIL)

Just as the BIP format treats each pixel of data as the separate unit, the band interleaved by line (BIL) format is stored by lines. Below figure shows the logic of how the data is recorded to the computer tape in sequential values for a four-band image in BIL format.

Band Interleaved by Line Format

Each line is represented in all four bands before the next line is recorded. Like the BIP format, it is useful to use if all bands of the imagery are to be used in the analysis. If some bands are not of interest, the format is inefficient if the data are on tape, since it is necessary to read serially past unwanted data.

Band Sequential Format

The band sequential format requires that all data for a single band covering the entire scene be written as one file. Thus, if an analyst wanted to extract the area in the centre of a scene in four bands, it would be necessary to read into this location in four separate files to extract the desired information. Many researchers like this format because it is not necessary to read serially past unwanted information if certain bands are of no value, especially when the data are on a number of different tapes. Random-access optical disk technology, however, makes this serial argument obsolete.

The band sequential format (BSQ) for storing remotely sensed data on nine-track, 8-mm tapes, and CD ROMs. An ASCII head or file contains all the information about the image, including date of acquisition, sensor system, sun elevation, sun azimuth, and resembling logic. Each band of imagery is stored as a distinct file composed of i rows and j column separated by an end of file (EOF) from all other data. Each volume (e. g. tape or CD ROM) ends with an end-of-volume (EOV) marker. Multiple volumes make up a multiple-volume set (Jensen, 1996) .

Band Sequential Computer Compatible Tap Format

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