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Observation Files

Document Version: 1.2 | Last Updated: February 2026

This guide explains how to view, browse, and download observation files (FITS images) from the Science Scheduler.

Overview

The Observation Files page provides access to all files captured during an observation. You can view metadata, preview images, and download files individually or in bulk.

Accessing Observation Files

There are two ways to reach the Observation Files page:

Via Projects (Recommended): 1. Navigate to Projects from the main menu 2. Expand your project to see targets and observations 3. Look for the folder icon in the Files column 4. Click the folder icon to open the Observation Files page

Via Observation Details: 1. Navigate to My Observations or find the observation in Projects 2. Click on a completed observation to view its details 3. Click the View Files button 4. The Observation Files page opens showing all captured files

File Grid

Files are displayed in a grid view showing:

  • Thumbnail preview of each captured image
  • Filename and capture timestamp
  • Filter used for the exposure
  • Exposure time in seconds
  • File size
  • File type badges - FITS or preview indicators

Use the search field to filter files by name or metadata.

FITS Metadata Display

Click on any file to open the metadata dialog, which displays:

Image Information

  • Dimensions (width x height in pixels)
  • Bit depth and data type
  • Filter and exposure time
  • Binning mode

Coordinates

  • RA/Dec in both sexagesimal (HH:MM:SS / DD:MM:SS) and decimal formats
  • Object name from FITS header
  • Epoch (typically J2000)

Quality Metrics

  • ADU statistics (mean, median, standard deviation, min, max)
  • SNR (Signal-to-Noise Ratio)
  • Background level and background noise

Note

HFR, FWHM, and star count values are available in FITS file headers (see Embedded Quality Headers below) but are not displayed as named metrics on the Observation Files page.

Embedded Quality Headers

Quality metrics are automatically embedded in FITS file headers during server-side processing. When you download a FITS file, the following headers are included (when available):

FITS Keyword Description
FWHM Median FWHM in pixels
FWHMARC Median FWHM in arcseconds
NSTARS Number of stars detected
IMGSNR Image signal-to-noise ratio
BGLEVEL Background level (ADU)
BGNOISE Background noise RMS (ADU)
IMGMEAN Image mean value (ADU)
IMGMED Image median value (ADU)
PXSCALE Pixel scale (arcsec/pixel)

These headers allow you to assess image quality directly in any FITS viewer without needing the web interface.

Understanding Quality Metrics

Quality analysis runs automatically after each FITS file is plate-solved successfully. If plate solving fails or quality analysis encounters an error, the file is still saved — quality analysis is non-fatal and never blocks processing.

Here's what each metric tells you and how to interpret it:

FWHM (Full Width at Half Maximum)

FWHM measures star sharpness — how spread out the star profiles are. Reported in both pixels and arcseconds.

FWHM (arcsec) Interpretation
< 2.0" Excellent seeing, sharp stars
2.0" – 3.5" Good conditions, typical for most sites
3.5" – 5.0" Mediocre seeing, consider reviewing focus and conditions
> 5.0" Poor seeing or focus problem — check autofocus logs

Tip

FWHM in pixels depends on your pixel scale. A 2.0" FWHM at 1.0 arcsec/pixel is 2 pixels, but at 0.5 arcsec/pixel it's 4 pixels. Arcsecond values are more comparable across different equipment.

SNR (Signal-to-Noise Ratio)

SNR is an overall image quality indicator. Higher values mean the signal (your target) is stronger relative to background noise. These values are for individual frames — stacking N frames improves SNR by a factor of sqrt(N).

SNR Interpretation
> 100 Excellent — sub-1% photometric precision, publication-quality data
50 – 100 Good — reliable photometry with a few percent precision
20 – 50 Adequate for most science; photometric error ~5–10%
10 – 20 Marginal — detection is solid but photometric accuracy is limited (~10%+)
3 – 10 Weak — object detected but data quality is low; consider longer exposures or more frames
< 3 Below detection threshold — signal is indistinguishable from noise

These thresholds are based on standard astronomical practice. For further reading, see ESO Signal, Noise and Detection, STScI SNR Estimation, and Boyce Astro SNR.

Star Count

Two star counts are reported:

  • Stars detected — total objects found by the detection algorithm
  • Stars measured — objects that passed quality filters (not saturated, not too faint, well-formed)

A significant drop in star count compared to previous frames of the same target may indicate cloud cover, fog, or dew forming on the optics.

ADU Statistics

ADU (Analog-to-Digital Unit) statistics describe the brightness distribution of the image:

Statistic What It Shows
Mean Average pixel brightness across the image
Median Middle value — less affected by bright stars than the mean
Std Dev Spread of pixel values — higher means more contrast
Min / Max Darkest and brightest pixel values

For a well-exposed image, the median should be above the noise floor but well below saturation. If the median is very high, the sky background is bright (twilight, moon, light pollution). If the max is at the camera's bit depth (e.g., 65535 for 16-bit), some pixels are saturated.

Background Level and Noise

  • Background level — the average brightness of the sky background in ADU
  • Background noise — the RMS noise in the background (excludes stars and the target)

Together these indicate sky conditions. A rising background level over the night may indicate increasing light pollution, twilight, or thin clouds scattering moonlight.

Pixel Scale

Pixel scale is the angular size of each pixel in arcseconds per pixel. This is calculated from the focal length and camera pixel size and is used to convert FWHM from pixels to arcseconds.

Capture Details

  • Camera name and settings
  • Telescope and focal length
  • Capture timestamp (UTC)
  • Software used for capture

Downloading Files

Individual Download

Click the download icon on any file in the grid to download it individually.

Download All (Batch Download)

The Download All button downloads all files from the observation to a local folder.

How it works:

  1. Click Download All
  2. Your browser prompts you to select a destination folder (using the File System Access API)
  3. Files download in parallel (up to 4 at a time) for faster completion
  4. A progress indicator shows download status
  5. The session is kept alive during long downloads to prevent timeouts

Requirements: - HTTPS connection required for batch downloads in Chrome - Modern browser with File System Access API support (Chrome, Edge) - For browsers without File System Access API support, files download individually as a fallback

Tips: - Large observations with many files may take time — the progress indicator tracks completion - Downloads continue even if you navigate to other tabs (session keep-alive is active) - If a download fails, you can retry individual files or restart the batch download

Download as ZIP Archive

The Download ZIP option creates a single ZIP archive containing all FITS files plus a metadata file. This is useful when you want a single downloadable package for an observation.

The ZIP archive includes:

  • All FITS files from the observation
  • An observation_metadata.json file with observation details: target name, timestamps, and per-file information (size, upload time, exposure index)

The ZIP filename follows the format observation_[target_name]_[date].zip.

Download Previews

The Download Previews option creates a ZIP archive of all preview PNG images from the observation. Preview images are lower-resolution representations generated during processing — useful for quick visual review without downloading full FITS files.

Download Calibrated

On the file detail page, the Download button includes a dropdown with two options:

  • Download Raw - The original file as captured
  • Download Calibrated - The calibrated version with dark subtraction, flat correction, and bias removal applied

The calibrated download option is only available when the file's calibration status shows Calibrated (a green chip). The first calibrated download may take a moment as the calibration is performed on-demand; subsequent downloads are served from cache.

If calibration is not available (no matching masters, calibration disabled, or calibration failed), the "Download Calibrated" option is grayed out with a tooltip explaining why.

In the file grid, calibrated files also show a green flask icon button for quick calibrated downloads.

Project Multi-Ownership

When an observation belongs to a project with multiple owners, all project owners can access the observation files. This enables collaborative workflows where team members share data from observations.