Externet Posted November 21, 2018 Posted November 21, 2018 Saw a report in television that japanese are measuring structural level irregularities in aging bridges with resolution of one milimetre from a satellite using its synthetic aperture radar. Wondering if I was half asleep during the report; I had to see it again. I was not asleep. That is their spectacular unbelievable claim. The program should be available as video-on-demand soon. ----> https://www3.nhk.or.jp/nhkworld/en/tv/scienceview/20181121/2015204/ 1
Externet Posted November 21, 2018 Author Posted November 21, 2018 Or mind boggling. Compared to the already surprising satellite highest resolution photography, focusing from such distance to a tiny spot shows how advanced techniques that are kept from general public knowledge may exist. If such has a civil application, military uses could map a relief of the grains of sand on a beach from such distance.
swansont Posted November 21, 2018 Posted November 21, 2018 People already do differential GPS to better than a centimeter. This doesn't seem that much different. The advantage of such a measurement is a lot of the errors cancel out — the radar return sees basically the same atmosphere as the original pulse, so that becomes a very small source of error, since changes that could affect the result have to be on a time scale of about a millisecond or less. 1 ms would be 300 km round trip. Not much atmosphere above 150 km to cause issues.
studiot Posted November 21, 2018 Posted November 21, 2018 I would be more inclined to question the value of such a measurement than its 'validity'. 1mm relative to what?
swansont Posted November 21, 2018 Posted November 21, 2018 1 hour ago, studiot said: I would be more inclined to question the value of such a measurement than its 'validity'. 1mm relative to what? Probably to a reference point that's not on the bridge, or at least not in the area where traffic is. Which is how regular surveying works, AFAIK.
studiot Posted November 21, 2018 Posted November 21, 2018 (edited) 14 minutes ago, swansont said: Probably to a reference point that's not on the bridge, or at least not in the area where traffic is. Which is how regular surveying works, AFAIK. I wish it were that simple, but thank you for the thought. Horizontal time lapse comparative photogrammetry is far cheaper and will yield far more (useful) information. Edited November 21, 2018 by studiot
Strange Posted November 21, 2018 Posted November 21, 2018 36 minutes ago, studiot said: Horizontal time lapse comparative photogrammetry is far cheaper and will yield far more (useful) information. Is "cheaper" for a single bridge? Does it make a difference if they are spread out over 400,000 km2 and thousands of islands?
studiot Posted November 21, 2018 Posted November 21, 2018 (edited) 8 minutes ago, Strange said: Is "cheaper" for a single bridge? Does it make a difference if they are spread out over 400,000 km2 and thousands of islands? Spread out after an atom bomb you mean? If the bridges are spread out then so will the reference points. How would you access and identify these? And what exactly is being measured, accurate to 1mm? Don't get me wrong, if true (which I doubt) that is a tremendous achievement. I am just asking the value of such a measurement. Edited November 21, 2018 by studiot
Strange Posted November 21, 2018 Posted November 21, 2018 9 minutes ago, studiot said: Spread out after an atom bomb you mean? Droll. But no. I'm just wondering if the cost saving (if there is one, rather than just a technology demonstration) is because a large number of bridges across a large area of mountainous terrain and multiple islands can be checked from satellite, rather than having to send a team of surveyors out to each one.
Externet Posted November 21, 2018 Author Posted November 21, 2018 Update; it is available now. All the program is enjoyable, but the subject surfaces by time stamp ~4:00 if preferred to go direct. ----> https://www3.nhk.or.jp/nhkworld/en/vod/scienceview/2015204/
studiot Posted November 21, 2018 Posted November 21, 2018 (edited) 58 minutes ago, Strange said: Droll. But no. I'm just wondering if the cost saving (if there is one, rather than just a technology demonstration) is because a large number of bridges across a large area of mountainous terrain and multiple islands can be checked from satellite, rather than having to send a team of surveyors out to each one. Just be glad that the country you live in has possibly the most rigorous bridge monitoring regime in the world, and even then problems still occur. A UK bridge is checked every visually 2 years by a bridge inspection technician checked in depth by a Chartered Engineer (The phrase within touching distance of every part of the structure is used in the specification). We have not seen the type of internal high tension failure that caused the recent Italian tragedy or the slightly older American one because of this type of inspection requiring testing of internal prestressing components. Measuremnet to 1 mm or 10mm or 100mm would nopt help in such a case. So once again I ask what are they measuring to 1mm and what is the value of that measurement? As to the cost of photgrammetry v satellite. How many £billions does the implementation and maintenance of such a satellite system cost compared to a few £thousand to buy the photogrammetry equipment outright or £100 per use to hire the kit? Finally my thanks to Externet for providing this information to discuss. Edited November 21, 2018 by studiot
Strange Posted November 21, 2018 Posted November 21, 2018 33 minutes ago, studiot said: How many £billions does the implementation and maintenance of such a satellite system cost compared to a few £thousand to buy the photogrammetry equipment outright or £100 per use to hire the kit? I haven't watched the video (as usual). Is the satellite built just for this? Or are they using an existing satellite?
Externet Posted November 21, 2018 Author Posted November 21, 2018 The report does not specify, or I missed it. Now available ----> https://www3.nhk.or.jp/nhkworld/en/vod/scienceview/2015204/ Time stamp ~4:00
Strange Posted November 21, 2018 Posted November 21, 2018 13 minutes ago, Externet said: Now available I will try and watch it at some point. It sounds interesting.
studiot Posted November 21, 2018 Posted November 21, 2018 (edited) The trouble with being in too much of a rush is Quote A UK bridge is checked every visually 2 years by a bridge inspection technician checked in depth by a Chartered Engineer This should ahve read A UK bridge is checked visually every 2 years by a bridge inspection technician and checked in depth by a Chartered Engineer every 6 years Sorry I wonder can the satellite detect loose bolts, which are sometimes seen of our inspections. Edited November 21, 2018 by studiot
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