5 ms·
They likely had a barometer. The very same method we use today to supplement the rather unsteady altitude reading from GPS. If they did this, the next question
by jzwinck 11y ago
They likely had a barometer. The very same method we use today to supplement the rather unsteady altitude reading from GPS.
If they did this, the next question would be how accurate their calibration was. Barometric altimetry was only about 20 to 50 years old at that time.
- rwmj 11y agoI guess that raises another question: how do they calibrate the barometer at all? I assume by taking one up a mountain. (And how do they know the height of the mountain? Using a sextant and simple trigonometry).
- jzwinck 11y agoThey could use a mountain. They could equally use a balloon (just not to 20k feet). British scientists by that time were knowledgable enough to extrapolate. You can read about the height of Everest and other Himalayas. There are some interesting stories about the lengths people (mostly British and Europeans) went to precisely determine their heights from ground stations. Once, they thought Everest was exactly 29,000 feet but thought this figure lacked gravitas so added two feet to make it sound precise. So you can imagine the British ballooners might have played with the truth a bit too.
- chrisseaton 11y agoWhy is altitude from GPS unsteady? Do you mean unsteady compared to latitude and longitude? Why would one dimension be less precise than the others? Something to do with the position of the satellites being in a kind of domed plane rather than all around you? My tactical GPS has a separate digital barometer to help it establish a GPS location more quickly. I've always wondered why.
- jzwinck 11y agoYes, compared to lat and long. A good 2D GPS fix is easiest when you have a few satellites in different compass directions, say one at each of N,S,E,W. But for 3D, it is impossible to see a satellite underneath you. You have a bunch of them above you, and you need to difference the times of their signals' arrival. For more, see here: http://gpsinformation.net/main/altitude.htm http://gpsinformation.net/main/altitude.htm
- dfc 11y agoI kind of giggled when i read "tactical GPS." I imagine the device is all black and is made by a company whose motto is some variant of "high speed low drag." Other than that what is the difference between a "tactical GPS" and a run of the mill GPS?
- chrisseaton 11y agoIt's a small, ruggedised GPS that interfaces with personal military radio systems such as Bowman. Tactical meaning used on a person, as opposed to something on a vehicle with a big antenna. These didn't say they had a barometer, which is why I made the distinction. I used them when I was in the Army. What is there to giggle about in any of that?
- 7402 11y agoFull respect if you used it in the army. The giggling was probably because the GPS was thought to be "tacticool" (http://www.urbandictionary.com/define.php?term=Tacticool http://www.urbandictionary.com/define.php?term=Tacticool) as opposed to tactical.
- dfc 11y agoThis is exactly what I was thinking. You do not see many comments from Tommy Tacticool on HN.