Hello GNU radio folks,
A few radio astronomer friends have had a very
active interest in GNU Radio, but
I’m aware of relatively few Radio Astronomy oriented
contributions to GNU radio.
This email is a request to start a discussion on
some requirements of Radio Astronomy and the
software support they would need.
The main GNU Radio enhancement items on my short
list are:
1) Averaging of spectra for long periods (minutes to
hours), while capturing every spectrum.
2) Writing average and transient spectra based on
internal and external events.
a) Maybe this already exists, but a spectrum message is
needed so that averaging can be separated from writing.
b) Transient event detection with spectrum (or time
sequence) passed to a writing thread.
c) When sudden increases of signal are noted, time
sequences would be written. (When auto-detected).
3) Keeping tracking of information associated with
the observing setup. There are large numbers of ancillary data
values needed to calibrate and map spectral
observations (geographic location, precise time, horn/antenna
azimuth, elevation
gains, device types used for the observations, flags
to indicate calibration spectra etc).
I’ve greatly appreciated the GNU Radio software and
excellent quality of the GRC and all the code I’ve seen.
I’ve extensively modified the ‘FFT sink' to optimize
for averaging and added a write component inside that code.
Writing inside averaging is probably a mistake, as
writing suspends data collection for a short time. I need to
learn
how to bring my code up to the GNU Radio quality
standards etc and put the existing code in GNU Radio
distribution.
Further, can we add a spectra message type in
GNUradio so that spectral can be passed to different blocks?
To show that good progress has already been made, but still needs
quality integration into GNU Radio,
three figures are attached. Using an AIRSPY (10 MHz
bandwidth) and GNU radio, I’ve mapped the Milky Way Galaxy in
Neutral
hydrogen (1420.406 MHz). It would be great if we can
get this functionality, with a few significant
enhancements, into the standard GNU Radio release.
Observations are just recorded steadily, and spectra
written every minute. I’ve left GNU radio recording sky
brightness for a week
and the system was still functioning well when I
returned. After the data are gathered, the 1 minute spectra are
calibrated and averaged. After averaging, the data
are plotted and mapped. All data are ascii format.
1) The first figure shows one 24 hour observation of
the Sky, averaging the signals every hour. The x axis is
velocity of the parts of the
galaxy observed and Y axis is intensity. The
telescope (horn) was left outside for a day, pointed south with
elevation of 29 degrees
above the horizon. The different wiggly curves show
different arms of the Milky Way Galaxy.
The thick blue and thick blue dashed lines are
observations of the Center of the Milky Way galaxy, but one is
24 hours
later than the other. These observations are made
with a home made horn antenna, with about 3x3 foot square
opening.
A few days of data were collected to observe much of
the northern sky: Image shows Right Ascension on the X axis,
which is the time of day in astronomical
coordinates. A 24 hour period is shown on the X axis. The Y
axis
is Declination ( Roughly the Geographic Latitude) of
the observation on the Sky.
The Dark red regions show the Milky Way galaxy. The
dark blue regions are away from the plane of our galaxy.
The top line is close to the north pole.
Final figure shows the Galactic Coordinate of the
same data.
The X axis is Galactic Longitude, with the center of
the Milky Way at Galactic Longitude = 0, Latitude = 0.
The Y axis is Galactic Latitude, with the plane of
the Galaxy at Latitude = 0.0, where most of the Hydrogen is
seen.
This is the very same data from the previous figure,
but with coordinates converted to show the flatness of the
galaxy more clearly.
Empty region is below the horizon and can not be
observed from my back yard. After the software is in GNU Radio,
hopefully someone in the southern hemisphere can
fill in the gaps.
All the code to do the plotting is in python, but
probably is not appropriate for GNU Radio.
What should be discussed is how to add a relatively
few additional book keeping and data recording
features to GNU radio appropriate for astronomy.
Thanks
Glen
Glen: