Viking VISAB Experiment Data Record (EDR)

EDR – Experiment Data Record

Instrument:Visual Imaging Subsystem Cameras A and B

PDS Data Set ID: VO1-VO2-M-VIS-2-EDR-V2.0DOI: 10.17189/1520132

For more information about VISAB EDR products, see the Volume Archive Document.

The Visual Imaging Subsystem Cameras A and B (VISAB) Experiment Data Record (EDR) data products have not been processed in any form other than organizing the original telemetry into raster formatted files and compressing the image data using a Huffman encoding algorithm.

A brief summary of the processing procedures needed to convert the EDR images to radiometrically and geometrically calibrated products is now presented:

  1. Viking Orbiter images can be radiometrically calibrated by converting the digitized signal received from the camera (DN value) into a quantity that is proportional to the radiance reaching the sensor. Each Viking Orbiter VIS camera was calibrated before flight. In addition, changes in the calibration over time have been estimated from analyses of images of deep space and dust storms. The radiometric calibration procedure applies additive and multiplicative corrections that account for the varying sensitivity of the vidicon across the field of view and over time. The calibrated values are proportional to radiance factor, which is defined as the ratio of the observed radiance to the radiance of a normally illuminated lambertian reflector of unit reflectance at the same heliocentric distance.

  2. Geometric calibration of Viking Orbiter EDR images removes electronic distortions and transforms the point perspective geometry to the original image into a map projection. The electronic distortions are barrel-shaped distortions from the electron beam readout and complex distortions from interactions between the charge on the vidicon face plate and the electron beam. The electron distortions are modeled by comparing the predicted locations of undistorted reseau marks with the actual locations on an image.

VISAB EDR products have the following file names:

Fnnnxss.IMQ

where:

nnn = orbit in which image was acquired

x = spacecraft that acquired the image

A = Viking Orbiter 1

S = Viking Orbiter 1

B = Viking Orbiter 2

C = Viking Orbiter 1, before orbit insertion

D = Viking Orbiter 2, before orbit insertion

X = Viking Orbiter 1, acquired in an orbit with more than 100 images

ss = sequence number for images acquired within one orbit

In ODE, EDR products have the following Product IDs:

FNNNXSS.IMQ