New data
We are happy to announce that we received another set of data. Commanding was performed on Friday instead of Thursday. This results in a loss of measurements that were planned on Thursday, however these measurements can be repeated next week.
Localization algorithm tested
We finally found time to test our localization algorithm. The algorithm takes the received frequency and the ISS position and velocity (based on TLE data) as inputs. From these values it calculates the real transmitter’s frequency and the position of the transmitter. The picture below shows a waterfall recording with a nice ground station transmission at approximately 9:17 to 9:25 on 437.8 MHz. Guess who did this this transmission 😉
The algorithm now iteratively estimates the origin of the signal, starting with two meausrements only (the two first of the pass). After 12 measurements, the algorithm localizes the transmission to the region around Prague, Czech. Republic. Since we know the true location of the transmitter, we know that this solution is not correct. The simple algorithm has always two solutions, one on the “left” side of the satellite pass, one on the “right” side of the pass. To find out which of the two solutions is the correct one, you need more information. Either by pointing the receiving antenna (not possible on the ISS, it is always pointing Nadir), or by having information of multiple passes. Luckily, the “secret” transmitter was active during the next pass as well and four additional measurements were taken into account. Including 16 measurements results in the solution on the opposite ground track side of the solution that was gained after 12 measurements. The true location of the transmitter is about 70 km west of this location, but we think that this accuracy is quite good for a first try, given the fact that it is only based on frequency data. We will now improve the algorithm, using more sophisticated solvers and increasing the frequency resolution (bandwidth resolution, which currently is only 2kHz) for better results.
Further GUI improvements
The GUI now has features to add text to the waterfall diagrams. With that you can add notes about the origin of signals (e.g. Radar system, Internal Noise, DC offset, …). The notes will be stored in the database such that we can work together on the identification of all signals in the waterfall diagrams
Plan for week 44
For week 44 we mainly do L band experiments. Additionally, we looked into AIS and ADS-B bands to see if we can investigate spectrum use of these bands, too.
