themisasi 0.8.1

reads and plots THEMIS ASI video data of aurora.

Themis ASI Reader

Read & plot 256x256 "high resolution" THEMIS ASI ground-based imager data, from Python ≥ 3.6.

It also reads the THEMIS ASI star registered plate scale, giving azimuth and elevation for each pixel.

Install

1. install cdflib, which only uses Numpy to read CDF:

   pip install -r requirements.txt
   

2. install this program

   pip install -e .
   

You can test the basic functionality by from the top cdflib directory:

pytest

[optional] Install Themis-ASI code and optional fov prereqs useful for merging and examing field of view (FOV)

python -m pip install -e .[fov]

Usage

One of the main ways analysts might use THEMIS-ASI data is by loading it into a 3-D array (time, x, y).

import themisasi.io as tio

dat = tio.load('~/data/thg_l1_asf_fykn_2013041408_v01.cdf')

THEMIS-ASI output xarray.Dataset, which is used throughout geosciences and astronomy as a "smart" Numpy array. The simple image data stack is obtained by:

imgs = dat['imgs']

dat.time contains the approximate time of each image (consider the finite exposure time). dat.x and dat.y are simple pixel indices, perhaps not often needed.

Loading calibration data gives azimuth, elevation for each pixel and lat, lon of each camera.

import themisasi.io as tio

dat = tio.load(fn='~/data/thg_l1_asf_fykn_2013041408_v01.cdf', 
               calfn='~/data/themis_skymap_fykn_20061014.sav')

now dat contains several more variables and metadata.

Download, Read and Plot THEMIS ASI Data

1. Get video data from Themis all-sky imager data repository
2. [optional] find plate scale if you want projected lat/lon for each pixel. These files are named *asc*.cdf or *skymap*.sav.

February 4, 2012, 8 UT Fort Yukon

1. Download data

   DownloadThemis 2012-02-04T08
   

2. [optional] get this camera plate scale If you want to just plot this calibration data:

   PlotThemis ~/data/themis/thg_l2_asc_fykn_19700101_v01.cdf
   

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', '/tmp')

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 ~/data/themis/thg_l2_asc_fykn_19700101_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 tests/thg_l2_asc_fykn_19700101_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 tests/thg_l2_asc_fykn_19700101_v01.cdf -lla 65 -145 100.

Notes

Themis site map (2009)

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.