reads and plots THEMIS ASI video data of aurora.
Project description
THEMIS GBO ASI Reader
Read & plot 256x256 "high resolution" THEMIS ASI ground-based imager data from Python. THEMIS ASI data are collected with the original 2002 design, using Starlight-Xpress Lodestar MX716 cameras with monochrome Sony ICX249AL imaging chips. A subregion from full-size 752 x 582 pixels (512 x 512 pixels) are 2x2 binned to 256 x 256 pixels and retrieved over USB 1.1 for disk storage.
This package also reads the THEMIS ASI star registered plate scale, giving azimuth and elevation for each pixel.
Install
- install
cdflib
, which only uses Numpy to read CDF:pip install -r requirements.txt
- install this program
pip install -e .
You can test the basic functionality by from the top cdflib
directory:
pytest
Usage
One of the main ways analysts might use THEMIS-ASI data is by loading it into a 3-D array (time, x, y).
Single time
This example is where the ASI video files are in ~/data/themis
, and the Gakona site is selected at the time shown.
import themisasi as ta
dat = ta.load('~/data/themis', site='gako', treq='2011-01-06T17:00:03')
This returns the camera image from Gakona camera closest to the requested time, and the 'az', 'el' calibration data, if available.
THEMIS-ASI output xarray.Dataset, which is used throughout geosciences and astronomy. Xarray may be thought of as a "smart" Numpy array, or a multidimensional Pandas array. A THEMIS image data stack is obtained by:
dat = ta.load(...)
imgs = dat['imgs']
dat.time
contains the approximate time of each image (consider the finite exposure time).dat.x
anddat.y
are simple pixel indices, perhaps not often needed.
Image + Azimuth, Elevation
Loading calibration data gives azimuth, elevation for each pixel and lat, lon of each camera.
import themisasi as ta
dat = ta.load('~/data/themis', site='gako', treq='2011-01-06T17:00:03')
If an appropriate calibration file exists, dat
additionally contains 'az', 'el', 'lat', 'lon' and so on to allow using data for multi-camera analyses.
Coordinate conversion (optional)
If desired, convert azimuth/elevation to ra/dec using pymap3d.
pip install pymap3d
and then from within Python:
import pymap3d as pm
rasc, decl = pm.azel2radec(dat.az, dat.el, dat.lat, dat.lon, dat.time)
Download, Read and Plot THEMIS ASI Data
Get video data from Themis all-sky imager
data repository.
The
plate scale
data is also downloaded.
The calibration files are named *asc*.cdf
or *skymap*.sav
.
Example: February 4, 2012, 8 UT Gakona
DownloadThemis 2012-02-04T08 gako ~/data
or via the API:
import themisasi as ta
ta.download('2012-02-04T08', 'gako', '~/data')
with the API, it is convenient to for-loop over many sites at the same time(s):
sites = ['fykn', 'gako']
for site in sites:
ta.download('2012-02-04T08', site, '~/data')
With the calibration data, verify that the time range of the calibration data is appropriate for the time range of the image data. For example, calibration data from 1999 may not be valid for 2018 if the camera was ever moved in the enclosure during maintanence.https://github.com/dib-lab/khmer/pull/1430
You can optionally download from within Python:
import themisasi as ta
ta.download('2012-03-12T12', 'fykn', '~/data')
get times in a file
the convenience function themisasi.io.filetimes(filename)
returns a list of Python datetime
in a file
Video Playback / PNG conversion
This example plays the video content.
Use the -o
option to dump the frames to individual PNGs for easier back-and-forth viewing.
The calibration file (second filename) is optional.
PlotThemis ~/data/themis/thg_l1_asf_fykn_2013041408_v01.cdf
Plot time series of pixel(s)
Again, be sure the calibration file is appropriate for the time range of the video--the camera may have been moved / reoriented during maintenance.
The pixels can be specified by (azimuth, elevation) or (lat, lon, projection altitude [km])
Azimuth / Elevation:
PlotThemisPixels tests/thg_l1_ast_gako_20110505_v01.cdf -az 65 70 -el 48 68
Latitude, Longitude, Projection Altitude [kilometers]: Typically the brightest aurora is in the 100-110 km altitude range, so a common approximate is to assume "all" of the brightness comes from a single altitude in this region.
PlotThemisPixels tests/thg_l1_ast_gako_20110505_v01.cdf -lla 65 -145 100.
Notes
Themis site map (2009)
THEMIS GBO ASI spectral response:
Articles
These articles give vital descriptions of THEMIS GBO ASI.
- Mende 2008 SSR
- color instrument based on Themis: Jackel 2014
Resources
- Themis GBO ASI site coordinates
- THEMIS GBO ASI plate scale
- THEMIS GBO ASI plate scale
- Themis GBO ASI data repository
- Themis GBO ASI mosaic (all sites together)
Matlab
The Matlab code is obsolete, the Python version has so much more:
readTHEMIS('thg_l1_asf_fykn_2013041408_v01.cdf')
data corruption
I discovered that IDL 8.0 had a problem saving structured arrays of bytes. While current versions of IDL can read these corrupted .sav files, GDL 0.9.4 and SciPy 0.16.1 cannot. I submitted a patch to SciPy to allow reading these files, which was incorporated into SciPy 0.18.0.
As a fallback, read and rewrite the corrupted file with the IDL script in the idl directory.
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