Data description

All-sky images

Images of all-sky imagers (ASI) are provided as zipped archives in raw jpg-format (sampling 30 seconds).

Directory structure: One folder per day and station

File format

Dataset	Temporal resolution	Image size	File size	File type	Filename
Hemispheric image	30 seconds	2112x2048 px	~150-200 KB/image	JPG	YYYYMMDD_HHMMSS_EXP.jpg

YYYYMMDD_HHMMSS corresponds to the timestamp when the image has been captured in UTC EXP corresponds to the exposure time of the image. During daytime a exposure time of 160ms is used. During full-moon nights also nighttime images with an exposure time of 80000ms are available.

Note: The first image after switching the exposure time (sunrise, sunset) should not be taken into considerations because of delays in setting image exposure time.

Quality remarks

Invalid images (broken downloads, empty images, ...) have been removed from the dataset. Moreover, images where faces of people are visible have been removed.

Any other disturbed images (e.g. due to birds, insects or just dirt) are kept in the database.

Meta data

For each station/camera there is

• a YAML-file providing meta data for each configuration change. The filename contains the timestamp of the latest change in configuration (could be a change in camera alignment or positioning). The file contains information on geographical coordinates, internal and external orientation and necessary mask file.
• image masks in binary png-files and mat-files.
• an example ASI image with an image mask overlay and image orientated to geographic north according to calibration parameters
• a keogram composite of all ASI images in the full data period.

Image processing

Python libraries for image handling are in preparation and will be soon published on Github

Locations

The yaml-files in the meta data directory provide the geographical coordinates for each station. See this map for an overview of all locations

Figure: Distribution of ASI and meteorological stations active in August 2022.