HST Data Handbook for ACS

2.3 Data Storage Requirements

---

Users are reminded to consider the large size of WFC exposures when allocating disk space for storing and reprocessing ACS data. Raw images, which serve as input to the calibration pipeline, have the sizes given in table 2.4.

Table 2.4: Size of raw ACS data for each detector.

Detector	Size of FITS file (Sraw)	X Pixels	Y pixels/chip
WFC (2 Chips)	68.7 MB	4144	2068
HRC (1 Chip)	4.4 MB	1062	1044
SBC (1 detector)	4.2 MB	1024	1024

 

These file sizes presume that both the SCI array and DQ array are populated with short integer values, but that the ERR arrays are NULL with all pixels having a value of zero. During processing, the SCI arrays are converted from integer to floating point values. The ERR array is also populated with floating point values. As a result, the final size of the calibrated images is much larger, as given in table 2.5.

Table 2.5: Final sizes of calibrated ACS data for each detector.

Detector	Size of FITS file (Sfinal)	X Pixels	Y pixels/chip
WFC (2 Chips)	168 MB	4096	2048
HRC (1 Chip)	10.5 MB	1024	1024
SBC (1 detector)	10.5 MB	1024	1024

 

While the size of the final calibrated HRC or SBC images is comparable to that of STIS or WFPC2, the ACS WFC images are over 16 times as large. To estimate the minimum amount of free storage, D_min , required for processing "n" associated ACS datasets, the following equation should be used:

where S_raw and Sfinal are the sizes of each raw and calibrated ACS dataset, respectively, as given in table 2.4 and table 2.5.

	Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu