Implementing accurate GPS deviation depending on systems would definitely encourage users to use bigger bombs and not the smaller ones. Also, 1m might be the difference between the bomb landing on top of the target, or the building that he’s hugging, which would mean no effect on the target.
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Regarding Beidou, there’s a newer version of that standards document you used (version 3.0 from 2021) here: http://www.beidou.gov.cn/xt/gfxz/202105/P020210526216231136238.pdf. It states that the “accuracy standard” is 9 m horizontal and 10 m vertical.
However, the standard is generally a minimum guarantee, which would probably be more lenient than the actual average performance. In an official news release, the average accuracy is stated to be 2-3 m (2.34 m specifically), though regrettably they do not specify whether it’s horizontal or vertical.
Sources (all in Chinese, unfortunately):
http://www.beidou.gov.cn/yw/gjdt/202211/t20221123_25168.html
Image from source:
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The standard used for BeiDou is the same standard used for the primary sources of the other systems which is 95% positional accuracy.
Spoiler
That is true.
On the other hand though, I just noticed in the same standards document that there is a separate service called the Precise Point Positioning (PPP) Service (described from page 19 onwards). That one is still a satellite-only system (as opposed to the Ground Augmentation System (GAS) Service that uses mobile communication information) and can achieve 30 cm horizontal and 60 cm vertical accuracy using BDS alone (there’s a weird BDS+GPS system with even higher accuracy, akin to Galileo’s HAS, but I doubt that the US would be open to allowing GPS augmentation in a hypothetical war scenario).
Table from page 21:
Could you look into BDS more and tell me what it is? That seems to be interesting
Uhhh, BDS is just the acronym for BeiDou System, if that’s what you’re asking?
Fair enough, I’ll incorporate this new data. I thought perhaps BDS is a completely different system for China, but it is not.
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What’s left is Quasi-Zenith and Glonass so far
If I’m interpreting their documents correctly, Quasi-Zenith (QZSS) provides three main services: the basic Positioning, Navigation, and Time Service (PNT); the Sub-meter Level Augmentation Service (SLAS); and the Centimeter Level Augmentation Service (CLAS). Of these three, CLAS is stated to suffer from 10 to 20 seconds of lag and should be limited to specific areas (source: https://qzss.go.jp/en/overview/services/sv06_clas.html), so I doubt it would be used for military purposes. SLAS might be usable, but it’s still said to suffer from time lag, though somewhat less and can be used for pedestrians, bicycles, ships, etc (source: Sub-meter Level Augmentation Service (SLAS)｜Service Overview｜QZSS (Quasi-Zenith Satellite System) - Cabinet Office (Japan)). To be honest, I’m not sure if QZSS is actually used for military purposes, they might just use basic GPS.
According to status reports from 2024:
PNT has a Root Mean Square User Range Error ranging from 0.56 - 1.02 m, but that doesn’t translate directly into horizontal and vertical errors (source: https://sys.qzss.go.jp/serv_report/SPO/Service%20performance%20report_for_1stH_FY2024_PNT.pdf)
SLAS has horizontal accuracy ranging from 0.59 to 2.29 m, and vertical accuracy ranging from 0.76 to 2.70 m, just eyeballing the data table (source: https://sys.qzss.go.jp/serv_report/SLA/Service%20performance%20report_for_1stH_FY2024_SLAS.pdf)
The source for CLAS is here: https://sys.qzss.go.jp/serv_report/CLA/Service%20performance%20report_for_1stH_FY2024_CLAS.pdf. I’m not going to calculate the results since there are even more data points here, but just a cursory glance suggests that accuracy is within 10 cm.
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It’s been said that the Japanese military uses US’ GPS in addition to Quasi-Zenith to provide more accuracy, so the numbers should be greater than the US’ precisions.
Yeah, I think you’re right that QZSS is also used. This IISS article says that their naval ships started using QZSS in 2019 as a backup for GPS. The remaining question is which mode they use it in. If they just use PNT, the accuracy may be marginally higher due to the larger number of satellites available (which allows for better dilution of precision). SLAS might be used at some installations, but as the source shows, there can be some variability in accuracy, perhaps due to time lag.
It should also be noted that right now the only GNSS weapons in the Japanese air tree are on the Thai JAS39C, which probably just used normal GPS in real life (though QZSS is apparently interoperable with GPS, so it may benefit from the enhanced precision from the PNT mode). QZSS will become more relevant when the Mitsubishi F-2 arrives in-game.
And to finish things off, here’s the performance standard for GLONASS: https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf. On page 42-43 the global average positioning error is listed as 5 m horizontal and 9 m vertical. There’s also a worst site positioning error of 12 m horizontal and 25 m vertical, but I don’t think we’ll need to worry about that.
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You’ve been wonderful, I appreciate your help. I think the last thing that needs to be done is some kind of primary source that the Japanese military relies primarily on US’ GPS. Especially if it looks like their own system is instead a back-up.
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From what I found, it seems that the JSDF uses (or is planning to use) multiple navigation systems in tandem to increase robustness. For example, page 8 of Defense Programs and Budget of Japan, Overview of FY2021 Budget Request says that they are developing a common receiver for signals from Michibiki (Japanese name for QZSS), GPS, and Galileo. For a more recent primary source, page 33 of the references to the Defense of Japan 2024 white paper by the Ministry of Defense says that the Ministry of Defense and the Self-Defense Force “will
promote the use of multiple positioning signals including Quasi-Zenith Satellite System (QZSS) and commercial satellites”. In game this could mean that their GNSS bombs would use whichever system that has the highest accuracy (from the sources we’ve got so far, probably Galileo).
It appears that the JSDF might not have fully integrated QZSS into their systems yet, though perhaps they may be using it on a case by case basis, like the ship example mentioned earlier. For a source of them using GPS, page 292 of Defense of Japan 2019 says that “the MOD/SDF has mounted
GPS receiving terminals on a large number of equipment”. Similarly, page 4 of this briefing memo of the National Institute for Defense Studies from 2017 says that they had been using GPS since 1993, before which they used TRANSIT since 1986.
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Well this became quite relevant now that Gaijin decided all GNSS weapons should have an up to 10m inaccuracy.
Though it doesn’t really hurt most bombs, it hurts the GBU-39, which is a particularly small bomb, the most. I read claims of submeter accuracy, apparently because it uses differential GPS (using ground stations) to enhance accuracy. But even without those, it’s currently a bit worse.
Like stuff like these pictures (from SDB brochure) should be otherwise statistically unlikely:
In game now:
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Hmm, that definitely seems to be too inaccurate. GPS SPS should have a 1.82 m horizontal accuracy (diameter of 3.64 m). Since the Leo 2 has a width of 3.7 m and the Abrams has a width of 3.66 m, it should be able hit the tank when aiming at the centre.
At least they have a line in the code they can easily tune now to real life, but as of right now every GNSS weapon has a 10m accuracy.
This article at least says SDB uses WADGPS, which from a little bit of searching allows submeter accuracy (or even less). Makes sense, because the SDB would be incredibly ineffecive if not almost directly hitting whatever it’s targetting.
Claims JDAM has a CEP of 13m, and SDB <4m. I can tell you however that these are outdated figures (article is from 2004). JDAM has a lower CEP than that 13m figure, but the JDAM manual is very much export restricted, so can’t be used. But you can probably find it. SDB likely is submeter nowadays (with the required infrastructure available).
2015 AF magazine:
Figure matches with the JDAM manual of the same year actually. They have accepted AF magazine as valid source (secondary I guess?) in the past. 13m CEP actually is also mentioned in the manual for GPS-denied zones when using GPS guidance in anti jamming mode, maybe that is where that comes from.
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JDAM should be 1.7meter.
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It possibly can go that low, maybe they also improved it more since 2015. But quoting JDAM delivery manuals, it is a 5m CEP. Might need to check it again, but I think the only figure like 1.7m was the TLE.
I recall a primary source for the F-2’s navigation module which was just a GPS + INS one.
Might try to find it, also have some secondary sources saying the XGCS-2 uses GPS, nothing primary on that though.
I also have some document somewhere talking about combining GPS with INS for better navigational accuracy, so i dont really think they use QZSS at all.
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