3 ms·

> The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcas

by tivert 3y ago

> The cm-level accuracy here is achieved by having two recievers, one fixed, one roving - with the fixed one acting as a base station that continuously broadcasts the "drift" in its fixed position as reported by the satellites - that's the error signal - deduct that and you've got improved position. https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS > The military had that for mobile battlefield units to improve accuracy, fixed ground base stations broadcasting fixes to missiles. Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. My understanding is the military has always had access to multiple GPS frequencies, which allow it to significantly reduce certain sources of error that single-frequency civilian units are subject to.

defrost 3y ago
> Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. It doesn't require the cooperation of "the enemy" - one side alone can have a mobile firing control station which parks up (assumes a fixed position) and broadcasts a DGPS signal in addition to other CnC comms to missiles that it fires and controls. > My understanding is the military has always had access to multiple GPS frequencies, They've also planned for continued functioning as best possible in case of full and|or partial loss of GPS frequencies. To recap, there's always been a coarse L1 GPS signal - that was delibrately made worse until 2000 by the addition of a keyed random clock error that required a daily key to revert (Differential GPS could fix that for anybody, the US Coast Guard broadcast a DGPS signal to "fix" that), there's always been a second L2 frequency that dual frequency users with both the coarse L1 daily key and the additional L2 key could use to improve accuracy with dual frequency tricks .. and, again, Differential GPS could improve that even more (by eliminating ionospheric errors, etc) - by the magic of Kalman Filters. There's a history of DGPS use here: https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS It's mainly focused on civilian (and US Coast Guard who apparently weren't "military enough" or something <shrug>) efforts to get military grade GPS via their own DGPS adventures ... but it was also the case that even the US military with dual channels and all the keys to enable real time reversal of broadcast errors could also benefit from increased accuracy via local theatre broadcast DGPS. Do I have sources for the US military use of DGPS in the late 1980s and 1990s? As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work.
- tivert 3y ago
  > Do I have sources for the US military use of DGPS in the late 1980s and 1990s? > As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work. After thinking about the range of DGPS and how that would impact how it would be used, I googled "himars dgps" and found this: https://www.hsdl.org/?view&did=448290 https://www.hsdl.org/?view&did=448290: > The Defense Science Board 1998 Summer Study Task Force on JOINT OPERATIONS SUPERIORITY IN THE 21st CENTURY > ... > As previously discussed, it will be possible in the 21St century to develop and globally deploy a military DGPS capability to any conflict area. The DGPS will contain anti-jam and other unique features to provide high assurance of signal availability and accuracy. In addition, the United States will have collected and updated global digital terrain elevation data (DTED) to 1-3 meter accuracy. The combination of real-time DGPS, digital terrain data, and highly accurate, space-based imagery (electro-optical/infiared/SAR) with ground moving target tracking capability, would make it possible to register fixed and moving targets on the battlefield to submeter accuracy. Rapid registration updates would also be possible using the dynamic collection capability of space-based imaging and tracking systems augmented perhaps with high altitude, long-endurance (HAE), unmanned aerial vehicle (UAV)-based sensor systems. > This registration and DGPS now make it possible to consider new families of high precision munitions such as the DGPS-guided SPB. As target location error is driven to submeter accuracy, even smaller and lighter but lethal, high-precision weapons could be possible. > .... > This capability was demonstrated during an effort undertaken in 1993 to investigate the possibility of achieving a three-meter CEP impact accuracy for the JDAM product improvement program. The technology inquiry pursued two possible solution sets: seeker improvements and/or navigation guidance improvements. Given that seekers have certain limitations, the navigation guidance improvement path was pursued. Two possible solutions to improve navigation error were considered: the civilian DGPS system approach or the military dual-frequency GPS receivers. The DPGS system employs pseudorange corrections generated by a GPS reference receiver. This approach is limited in range since the user must remain within line of sight of the ground receiver. In contrast, the military GPS receivers are capable of using ionosphere-free pseudorange measurements that extend the range to greater than 1,000 miles. In this case, range is a function of maintaining visibility with the satellite that is receiving corrections fiom a regional ground station. > Using the latter approach in an Air Force-sponsored Joint Direct Attack Munition System Program entitled "Exploitation of DGPS for Guidance Enhancement (EDGE)," four ground stations were emplaced more than 1,000nm fiom the Eglin Air Force Base test range. Navigation corrections from the distant network were uploaded to a modified GBU-15 -a 2,000 pound glide bomb. In a release at 25,000 feet above an overcast, 1.4 miles from the target, the unpowered weapon hit within 2 meters of an aim-point.

by tivert 3y ago

defrost 3y ago

> Do you have a source for that? Because it doesn't make any sense to me. The enemy is unlikely to be willing to site a DGPS base station nearby to increase the accuracy of missiles being used to attack it. It doesn't require the cooperation of "the enemy" - one side alone can have a mobile firing control station which parks up (assumes a fixed position) and broadcasts a DGPS signal in addition to other CnC comms to missiles that it fires and controls. > My understanding is the military has always had access to multiple GPS frequencies, They've also planned for continued functioning as best possible in case of full and|or partial loss of GPS frequencies. To recap, there's always been a coarse L1 GPS signal - that was delibrately made worse until 2000 by the addition of a keyed random clock error that required a daily key to revert (Differential GPS could fix that for anybody, the US Coast Guard broadcast a DGPS signal to "fix" that), there's always been a second L2 frequency that dual frequency users with both the coarse L1 daily key and the additional L2 key could use to improve accuracy with dual frequency tricks .. and, again, Differential GPS could improve that even more (by eliminating ionospheric errors, etc) - by the magic of Kalman Filters. There's a history of DGPS use here: https://en.wikipedia.org/wiki/Differential_GPS https://en.wikipedia.org/wiki/Differential_GPS It's mainly focused on civilian (and US Coast Guard who apparently weren't "military enough" or something <shrug>) efforts to get military grade GPS via their own DGPS adventures ... but it was also the case that even the US military with dual channels and all the keys to enable real time reversal of broadcast errors could also benefit from increased accuracy via local theatre broadcast DGPS. Do I have sources for the US military use of DGPS in the late 1980s and 1990s? As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work.

tivert 3y ago
> Do I have sources for the US military use of DGPS in the late 1980s and 1990s? > As an Australian involved in international high precision surveying I have vague recollections of articles stating as much in Scientific American type journals of the day and various AGSO publications .. anything else that I might of seen via some kind of five eyes agreement I'd have to really dig about to find and then dig even further to find if it's now in the public domain .. way too much work. After thinking about the range of DGPS and how that would impact how it would be used, I googled "himars dgps" and found this: https://www.hsdl.org/?view&did=448290 https://www.hsdl.org/?view&did=448290: > The Defense Science Board 1998 Summer Study Task Force on JOINT OPERATIONS SUPERIORITY IN THE 21st CENTURY > ... > As previously discussed, it will be possible in the 21St century to develop and globally deploy a military DGPS capability to any conflict area. The DGPS will contain anti-jam and other unique features to provide high assurance of signal availability and accuracy. In addition, the United States will have collected and updated global digital terrain elevation data (DTED) to 1-3 meter accuracy. The combination of real-time DGPS, digital terrain data, and highly accurate, space-based imagery (electro-optical/infiared/SAR) with ground moving target tracking capability, would make it possible to register fixed and moving targets on the battlefield to submeter accuracy. Rapid registration updates would also be possible using the dynamic collection capability of space-based imaging and tracking systems augmented perhaps with high altitude, long-endurance (HAE), unmanned aerial vehicle (UAV)-based sensor systems. > This registration and DGPS now make it possible to consider new families of high precision munitions such as the DGPS-guided SPB. As target location error is driven to submeter accuracy, even smaller and lighter but lethal, high-precision weapons could be possible. > .... > This capability was demonstrated during an effort undertaken in 1993 to investigate the possibility of achieving a three-meter CEP impact accuracy for the JDAM product improvement program. The technology inquiry pursued two possible solution sets: seeker improvements and/or navigation guidance improvements. Given that seekers have certain limitations, the navigation guidance improvement path was pursued. Two possible solutions to improve navigation error were considered: the civilian DGPS system approach or the military dual-frequency GPS receivers. The DPGS system employs pseudorange corrections generated by a GPS reference receiver. This approach is limited in range since the user must remain within line of sight of the ground receiver. In contrast, the military GPS receivers are capable of using ionosphere-free pseudorange measurements that extend the range to greater than 1,000 miles. In this case, range is a function of maintaining visibility with the satellite that is receiving corrections fiom a regional ground station. > Using the latter approach in an Air Force-sponsored Joint Direct Attack Munition System Program entitled "Exploitation of DGPS for Guidance Enhancement (EDGE)," four ground stations were emplaced more than 1,000nm fiom the Eglin Air Force Base test range. Navigation corrections from the distant network were uploaded to a modified GBU-15 -a 2,000 pound glide bomb. In a release at 25,000 feet above an overcast, 1.4 miles from the target, the unpowered weapon hit within 2 meters of an aim-point.