One quick observation I've noticed over the last week or so of measuring the returns from GRAVES via the ISS is that to get a strong signal I need ISS to be at 20 degree elevation angle. The pass yestersay at around 19:20 (local) I only got the following short detection:
In order to investigate why ISS was only detectable in a small amount of the pass I made the following graph:
The areas in blue are outside of the nominal azimuth & elevation pattern of the transmitter at GRAVES. Hence it is quite obvious why only a small part of the pass I managed to detect ISS. There was an earlier pass which had an elevation of 5 degrees to me here, which I didn't detect at all. If I make a plot for that pass then I get the following:
From the graph it is clear that ISS would have only been illuminated briefly and when combined with the extreme range (and local trees/houses/etc) would make it difficult to detect it.
The things I intend to investigate further are:
- If H-polarisation improves the signal-to-noise (ideally I'd do this using 2 identical sets of antennas and receivers but that would have to wait a while).
- Create a program which analyses the data collected and detects all the meteors/planes/etc and saves the 'interesting' data to be further analysed.
- Use the program I've developed to make the graphs above, be able to search for suitable times for me to attempt to detect the moon.
As an aside I've ordered the parts to make the frequency doubler which is necessary to improve the frequency stability of the RTLSDR dongles and hopefully allow me build a 2 (or maybe more) channel coherent receiver.
One of the other projects I'm currently looking at is building an X-ray telescope to be launched on a high altitude balloon. To be honest calling it an X-ray telescope is a bit grandiose, it'll be a 1 pixel detector! Anyway the first stage of the design process is to see what the atmospheric attenuation of X-rays is like. The graph below shows the altitude at which
0.5,
0.1 and
0.01 of the incident radiation is left.
The X-ray absorption data (for O2, N2, Ar) is from "AD-A278 139, NBS Circular 583" and the atmospheric model is from the C implementation of
NRLMSISE-00 which returns the number density for O2, N2 & Ar. In order to check that I've not made any blunders, I compared with the only other X-ray atmospheric graph I could find
here in fig 2.4, page 46. Although the line for
0.5 agrees well, the other lines do not. In order to double check my answers I tried using the classic 1976 atmospheric model (which just returns the density of air) and the X-ray absorption data for air. Using these new set of data I get a very similar graph to that above (and get very good agreement at sea level which I also check with NIST). I'm unsure how to proceed at the moment with this, but will start to look at some of the other issues, such as energy resolution, collimation, weight, power, etc.
