Dear Thorsten, all,
Thanks for your responses - I will try to address some below, but others may require a further document or discussion at our July meeting. As you will note, some questions require the response of parties who are not yet part of this email chain. I've asked the SE40 chair to establish a reflector or forum so we capture the exchange for all to follow.
Also, can you kindly reference the document when you offer comments? - Iridium has provided two documents for discussion on this subject (SE40(23)012, and SE40(23)0xx to be renumbered).
- Evaluation with DataReduction Software:
- Iridium agrees that the comparison of results will need further discussion in order to identify the differences in values. During our processing, we used a few different “assumptions” but were unable to replicate the Leeheim data exactly (these assumptions are not documented in the BNetzA measurement report). The results in Table 1 (SE40(23)012) were made (I believe) with the same combination of measurement-files, background-files, and calibration files as you kindly provided in the report and in earlier exchanges – but I will confirm this.
- Iridium agrees that we should examine a single measurement in more detail, to identify the difference in outcome.
- (N/A – Iridium believes it used the same approach)
- Note that Iridium was not able to replicate the max (mean_SJy) values for each pass at the every first stage (see 3.1, SE40(23)0xx), or the calibrated files from the raw files (section 3.3, SE40(23)0xx), indicating a problem in this first stage of processing.
- Finally, please note that we expect the overall result will be slightly different, as we combined the different measurements differently for reasons highlighted in SE40(23)0xx, including balancing the choice of orbit planes.
- Evaluation with EPFD Software:
- The original scripts were developed by Prof Jessner (MPIfR), and later developed by Thales/ANFR within SE40.
- I need to consult others to answer your detailed questions here, and I hope to provide an answer ahead of our meeting.
- When is the goal reached?:
- I’m afraid the Iridium document has given the wrong impression, when I read your statement: The [Iridium] document says that the EPFD evaluation does not fulfil the requirements, because there is a disproportion between day and night measurements and even/odd planes. Iridium believes the measurements are valid and useful, but we need to agree how to use them. We expect a difference between day and night, and between even and odd planes – this is a reflection of the traffic on respective satellites, and hence the out-of-band signals generated. However, we need to agree within SE40 how to generate a comparable average that will be useful moving forward, and also how future measurements are taken.
- Even given the points we identified, the overall results in the Leeheim calculations and the Iridium calculations are close (6.6dB vs 6.1dB).
- Within our discussion, Iridium hopes to (i) identify the source of the differences (particularly in point (1) above), (ii) find consensus to record the results in an ECC Report, and (iii) agree on the specification of future measurements. We are not advocating further measurements now, but we anticipate further satellite upgrades which will require measurement, perhaps later in 2023/24.
I hope this helps clarify the issues. Our meeting in July will help to move this along, but we can also exchange further information as needed.
From: [email protected] <[email protected]>
Sent: Thursday, June 15, 2023 3:10 PM
To: Michael Thompson <[email protected]>; [email protected]; [email protected]; [email protected]
Cc: Jaime Afonso <[email protected]>; [email protected]; [email protected]; [email protected]; [email protected]; Jaime Afonso <[email protected]>; [email protected]; [email protected]; [email protected]; [email protected]
Subject: AW: EXTERNAL:information document - Report on IRIDIUM unwanted emissions 1610.6 – 1613.8 MHz - 2022
Dear all, dear Mike,
I would like to coment/question some oft he points in your document!
- Evaluation with DataReduction Software:
Regarding the differences in the results of the DataReduction package (thresholds exceeded), the document shows a table with differences in the Iridium<->Leeheim calculated results (Table 1: Summary of the satellites observed in the 2022 measurement campaign)
In general it isabsolutely necessary, that when presenting results, you explain in detail how you arrived at those results. In the same way we do it in our Leeheim reports. Otherwise nobody can validate your results !!!
In relation to your Table 1: "Summary of the satellites observed in the 2022 measurement campaign", I must therefore specifically ask:
!!! Did you use exactly the same combination of measurement-files, background-files, and calibration files as shown in our report with exactly the same parameters (meas-times, backg-times, star fuxes etc) ???
If you can confirm this, I think we should pick a single measurement and calculate it in parallel to find out why and where these differences occur.
If you not used exactly the same files/parameters as shown in our report, you should exactly present how you did your calculation !!!
2 Evaluation with EPFD Software:
Concerning the EPFD evaluation i also would like generally to say something:
Some time ago these script where modified. I don't know who did this.
As a result the calculation was splitted in two parts: OOB-evaluation and Noise-evaluation.
I could not find anything in the existing recommendation about why the same algorithm should not be used for both evaluations (OOB and Noise).
Or otherwise: !!!! What is the difference between these two calculations and as a conclusion ----> which additional measurements have to be performed to feed the noise part of the EPFD-scripts ???
Does the Noise-part (1583)
- require only a point-backgound measurement ?,
- does it require a hemisphere measurement without satellite ?
- does it require a elevation corrected hemisphere measurement without satellite ?
(which means you need 2 noise-measurements with additionell point background measurement)
I assumed the latter to be the case, but it is not described anywhere, and there is no corresponding requirement or measurement specification for the Leeheim measurements concerning this.
Also it must be clear how many of those noise measurements the EPFD-Noise package needs, and when those measurements have to be made.
The document says : " ... we noted that a few noise passes did not have a background spot measurement" !!!
Of course they do not, because for evaluating the measurements with the DataReduction Packet, you do not need this. And you not needed it fort he "old" EPFD evaluation.
If it is now needed, we should have been informed before we did the measurements - > after reprogramming the EPFD software, a new measurement specification has obviously not been created to this day.
This was the reason why we did use old noisepass measurements with addional backgound point measurements which we performed coincidentally in the past.
In my opinion, piecing together a file (using a 25 second window from the measurement) like you did is not a good solution.
Furthermore if you be aware what the EPFD Noise-Part exatly does and what input it needs, you need to carefully examine the uncertaintys of the EPFD SW by using Leeheim measurements.
I have already pointed out that even with small changes in the average of the input values (e.g. 20 Jy), which is definitely within the measurement inaccuracy of our measuring station, the resulting DEC factor varies by 3 dB when considering the EPFD noise.
The measurement uncertainty always increases as the measured values move towards the sensitivity of the system.
In case oft he Noise-measurements we try to measure the sensitivity itself.
The current EPFD-Noise package seem to significantly reinforces this uncertainty.
All of these points must be examined and clarified before you can believe to get a trusting result from the EPFD evaluation.
I don't see this now, and a comparison to old EPFD-evaluation is definitly not reliable.
- When is the goal reached?
The SE40 should also clarify what is the ultimate point concerning the question, when the distortions are acceptable.
The document says that the EPFD evaluation does not fulfill the requirements, because there is a disproportion between day and night measurements and even/odd planes...
I agree with that point. But to get rid of this problem, there has to be made an measuement-campaign with a proper amount of measurements from all planes in the same amount for day and night. Which goes along withs an enormous measurement campaign with lots of night-time measurements and dependend on the constraints (measure same satellites day night , min elev, at which day and night hours...) it would also take a very long time to get satellites of all the planes and get all this done.
If the exceeding tresholds produced by the Data-reduction package is a point that has to be fulfilled, then in the first point it is only nesseccary to look at the satellites with the higest distortions, That means day-measurements of even planes. Odd planes and night measurements are not of importance in this view.
Or should it be possible that the EPFD-evaluation (if it is working proper someday) fulfill the requirements, while single measurements from the DataReduction evaluation does not !?
As far as all this is not cleared i only see reliable and comparable results in the evaluation of the exeeding tresholds using the DataReduction part.
So i definitely agree with the summary in this document: "...further development of a specification for OOB measurements Is proposed."
A further development of a specification for OOB measurements especially for the EPFD calculation is absolutely necessary!
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