NICMOS Data Products

• Science image.
• Error array.
• Quality flags array.
• Samples array.
• Integration time array. Each downlinked readout is always represented by these five arrays (Figure 13.4). Multiple readouts in the same dataset (e.g., MULTIACCUM data) are represented by repeated sets of these five arrays (Figure 13.5). It is expected that compact FITS representations will be available to store arrays in which all elements have the same value.

  In the basic NICMOS data format, shown in Figure 13.4, each readout is represented by 5 arrays, each as a separate extension in the FITS container file. Any of the five arrays may be accessed by specifying its extension number: for example to access the data quality flags, specify the third extension.

Figure 13.4: Data Format for ACCUM, RAMP, BRIGHTOBJ and ACQ Modes

Error Array

Quality Flags Array

Samples Array

• For data where multiple samples of the array were obtained during the integration, the samples array denotes the number of samples for each pixel in the corresponding science image.
• When multiple integrations are combined to produce a single image, the samples array will contain the number of samples retained at each pixel. Note that this implies that the original number of samples information is not propagated forward into combined images.

The MULTIACCUM mode (Figure 13.5) produces multiple images. The file structure for such a dataset consists of a lattice of the 5 image arrays which are created for each readout, as shown in Figure 13.5.

Figure 13.5: MULTIACCUM Data Format

FITS File Format