Apzip Online

: Detector reads are converted into difference images (the first read plus difference images) to reduce dynamic range.

The theoretical maximum compression for APOGEE's noise levels and bit depth is approximately 2.6. In practice, APZIP’s compression of ~2.0 is considered as good as can be expected for the specific astrophysical data it handles. : Detector reads are converted into difference images

: An average difference image is computed and subtracted from all difference images, resulting in "residual" images that are easier to compress. : An average difference image is computed and

: Compressed files generated by APZIP are saved with the .apz extension. The APOGEE instrument produces roughly and up to

The APZIP procedure uses a three-step custom algorithm to achieve an average compression factor of approximately .

The APOGEE instrument produces roughly and up to 100 GB per night . APZIP was created to speed up data transfer from the Apache Point Observatory to the Science Archive Server (SAS) and to minimize overall disk usage. It compresses raw data cubes by taking advantage of the fact that successive reads of the detector arrays are highly similar. 2. Technical Compression Algorithm