# Accessing Raw and Calibrated Images

Contents

## Data Lab

Astro Data Lab access to raw and calibrated images is now available.

Raw and Calibrated Legacy Survey images are available from the NOIRLab Astro Data Archive through the web portal (https://astroarchive.noirlab.edu/portal/search/). The input data used to create the stacked images, Tractor catalogs, etc. comprise images taken by the dedicated DESI Legacy Imaging Surveys project, as well as other images from the NOIRLab telescopes.

## Web Interface

Warning: these instructions are still being updated.

1. Query the NOIRLab Astro Data archive.
2. From the menu of "Available Collections" on the left, select the desired data release (e.g. LS-DR9).
3. Under "Data products - Raw data" check "Object".
4. Optionally, you may select data from specific filters, or restrict the search by other parameters such as sky coordinates, observing date, or exposure time.
5. Click "Search".
6. The Results page offers several different ways to download the data.

## API Query

Warning: these instructions are still being updated.

Following the organization of the Stacked images, Raw and Calibrated images are organized by survey brick, which are defined in the file survey-bricks-dr9.fits.gz for DR9. Both the main Tractor catalogs and Sweep catalogs include the BRICKNAME keyword (corresponding to <brick> with format <AAAa>c<BBB>).

For the calibrated images, filenames can be retrieved from the IMAGE_FILENAME keyword in each brick from legacysurvey-<brick>-ccds.fits. Additionally, each calibrated/<AAA>/<brick> contains an ASCII file with a list of EXPID and IMAGE_FILENAME (legacysurvey-<brick>-image_filename.txt). EXPID contains the exposure number and the CCD name with the format EXPNUM-ccd. There is one entry per CCD. Often, multiple CCDs from a given file are used so there are fewer unique filenames than the number of CCDs. Each legacysurvey-<brick>-image_filename.txt file contains the number of unique images in the last row (File Count).

Note that the weight map images (the oow files) are in the same units as $$1/\mathtt{skyrms}^2$$ in the survey-ccds-<camera>-dr9.fits.gz files (documented above). But, these images need to be multiplied by both gain and exptime to retrieve units of electrons (for <camera> of mosaic or 90prime).