Lowell Calibrated Data Collection Overview

Data Abstract
=============
We obtained images of the (65803) Didymos system and supporting calibration
images with the Lowell Discovery Telescope (LDT) through a VR filter. These 
images were taken in order to determine the orbit period of Dimorphos, the 
satellite of Didymos. This collection consists of the Lowell calibrated images,
the supporting calibration images: master bias frame images, and master flat field images,
and the reference star PNGs.


Data Set Overview
=================
Raw image data (see data_ldtraw collection) are calibrated in three steps: (1) all images are 
trimmed down to just the useful part of the array as specified in the TRIMSEC 
header keyword, (2) a median combined master bias frame is subtracted from each 
flat field and sky image, and (3) a median combined, normalized flat field is 
divided into each sky frame. The master flat field is normalized by the median 
pixel value in the combined flat frame.

Naming Convention
=================
Calibrated images consist of a single fits file containing the raw 
image and an associated XML file. They are named according to the following 
convention.

lmi_<yyyymmdd>_<image counter>_<product type>_<version>.<ext> 

where: 
lmi refers to the Large Monolithic Imager instrument 
<yyyymmdd> year, month, day of observing session in UT

<image counter> four-digit image counter for observing session, reset for each 
night of observation, with counter starting at 0001.

<product type> defines product as one of the following types: raw or cal (for 
calibrated)

<version> the version of the data product. ex “v1” or “v2”.

<extension> the file extension. “.fits” for fits file format, “.xml” for the 
PDS label.

Ex. lmi_20201217_0157_cal_v1.fits is a calibrated image product for a 2020-12-17 
observing session. It is the 157th image generated on that UT date.

Reference Star PNGs
====================
For each calibrated image there are two associated PNGs of reference stars. 
One is the astrometry reference and the other is the photometry reference.

They are named according to the convention: 
<cal fits filename>_<product_type>_<version>.png where:

<cal fits filename> calibrated image fits filename as defined above. 
Ex. lmi_20201217_0062_cal

<product type> defines product as one of the following types: 
1) astro – astrometry reference 2)  photo – photometry reference

<version> the version of the data product. ex “v1” or “v2”
        
These PNGs are referenced in the calibrated image label via 
File_Area_Observational_Supplemental.

Master Bias and Flat Field Frames
=================================
For each observing session the calibrated images are generated from the raw 
images using master_bias.fits and master_flat_vr.fits calibration frames. 
The “vr” string in the master flat field name refers to the broadband filter 
in which the observations were obtained. 

master bias files are always named master_bias.<extension> where 
<extension> the file extension. “.fits” for fits file format, “.xml” for the 
PDS label.

master flat files are always named master_flat_vr.<extension> where 
<extension> the file extension. “.fits” for fits file format, “.xml” for the 
PDS label.

Although the filenames are hardcoded, each product can be referenced in PDS using the
logical identifier (LID) in the XML label. This logical identifier is unique for each 
PDS data product. The LID for the master bias and master flat field frames will contain 
the YYYYMMDD string corresponding to the observation date in which the master files were used.