I am wondering what the best tool is to compute the distance between two benchmarks first set in the early 1920s. Ideally I'd like to compute the distance using 1920s coordinates, compare that to the published distance, and finally compare it to modern measurements.
Backstory: I have some http://www.otherhand.org/home-page/physics/historical-speed-of-light-measurements-in-southern-california/&apos ;">web pages on the work Albert Michelson did on measuring the speed of light in Southern California in the 1920s, a supremely big deal at the time. His main work consisted of bouncing a light beam between the observatory on Mount Wilson and a mirror located on another mountain about 22 miles away. To support his work, Michelson enlisted the assistance of the US Coast and Geodetic Survey to precisely measure the distance between the two locations and set benchmarks. The survey was rather amazing in its own right and http://www.otherhand.org/wp-content/uploads/2012/03/A-Geodetic-Measurement-Of-Unusually-High-Accuracy.pdf&apos ;">is described here. The benchmarks still exist as Michelson (EW1861) and Antonio (EV3805).
The data sheets show the easily accessed Michelson benchmark was last visited in 1995 by the NGS, so that's probably a pretty good position. However the Antonio benchmark, with stupidly difficult access, was last visited by surveyors in 1950. This (unfortunately!) presented me with a compellingly attractive target as part of the GPS on BMs program. As expected, the hike up to the Antonio BM with the necessary equipment was pretty miserable, and the placement of the tripod on top of the 3-1/2 foot tall concrete pier was.....challenging, but I pulled it off last month. I submitted to OPUS-Share using the final satellite data and obtained https://www.ngs.noaa.gov/OPUS/getDatasheet.jsp?PID=EV3805&apos ;">this solution which I'm quite pleased with.
What I'd like to do is compare the distance measured between the two benchmarks in the 1920s with the distance obtained in more contemporary times. The reference I listed above to the 1922 survey gives levels of accuracy but oddly, not the absolute measurement. However Michelson, in one of his published papers gives a distance of 35,385.5 meters. That smells like a rounding to the nearest tenth, but I'm not certain.
I could likely get permission from the Mt. Wilson observatory to set up my gear on the Michelson BM and do a measurement there but I'm inclined not to attempt it. Since Michelson's era, a number of pine trees have grown to surround the site and I know my 5700 would not provide decent results in that situation. Thus my inclination to take the NGS 1995 data as good.
So I'd need to bring the Michelson 1995 coords up to the present and figure the distance to mine, or transform mine back to 1995 and compare using those. Or maybe both. Ultimately, it allows for a comparison between the amazing 1920s measurements and current to see if there's been any significant shift in the benchmark distances. I'm not expecting a lot as they should be both on the same edge of the Pacific Plate but I am curious.
Any suggestions as to which of the myriad of NGS tools might work best for this would be appreciated. It's just a notch above my pay grade (not that I'm getting paid).
The tool to get NAD83 values to the same epoch is probably HTDP on the NGS Toolkit pages.
I don't think HTDP deals with NAD27. You could try NADCON but I wouldn't rely on NAD27 to be particularly accurate in any case.
What you want is mark-to-mark distances. For a start, I'd take the NAD83 coordinates transformed to the same epoch, and use the elevations from the data sheets, plus whatever tripods or tower heights they used in the experiment. The elevations won't be particularly accurate, but good enough considering that the difference in elevations is small relative to the overall distance.
Transform lat-lon-height coordinates to XYZ (HTDP can do that along with the other work) and do a 3-dimensional Pythagorean hypotenuse for the path distance.
Now let's see what the experts say.
OtherHand, post: 455000, member: 12932 wrote: Michelson benchmark was last visited in 1995 by the NGS, so that's probably a pretty good position
I don't think they got any new data in 1995. The position is listed as
NAD 83(1992) EPOCH - 1991.35
which I think means they re-ran the least squares adjustment in 1992 using the old triangulation measurements for these stations that had no GPS data, and GPS positions on stations where they did.
The 1995 recovery report meant that NGS or some organization that reported to NGS said it was still there. Sometimes an agency that had no reporting code of their own sent the report in and it appears as NGS who then posted it for them.
Like Bill says above, HTDP is probably your best bet.
BUT, considering the crustal dynamics (and uncertainties) of that area, I doubt that you can expect much in the way "accuracy" (or is it precision).
Differential movement between these points is rather significant, and episodic displacement due to earthquakes might not be well modeled that far back.
Loyal
OtherHand; it would be nice if you could give me a reference to the paper you say that Dr. Michelson said the distance was 35,385.5 meters.
This base line was adjusted in 1990 (also in 1923+ by hand) by Cheryl Malone of NGS because Prof. Dave Jackson and one of his students
Mr. Zhengkanh Shen were interested in this also. I was assigned to help both of these people (Prof. Dave Jackson was a good friend of mine so
it just fell into place).
The adjusted distance (using the 1923 data) was 33,666.926 +/- 0.042 m
That distance was from Pasadena East base to Pasadena West Base.
I might have more data and I will look tomorrow. I do have a copy of all 1923 field data.
JOHN NOLTON
Nice catch on the date of the Michelson benchmark. I just assumed when the NGS is listed as the reporting agency, they would have actually done something in 1995.
Michelson wrote of the benchmark distance twice that I've seen, linking to the articles and their original page numbers:
http://www.otherhand.org/wp-content/uploads/2012/03/Preliminary-experiments-on-the-velocity-of-light-1924.pdf&apos ;">??Preliminary Experiments on the Velocity of Light?, A.A. Michelson, 1924 on page 260. This first mention lists the distance as 35,385.50 meters, so perhaps no rounding here.
http://www.otherhand.org/wp-content/uploads/2012/03/Measurement-of-the-velocity-of-light-between-Mt-Wilson-and-Mt-San-Antonio-1927.pdf&apos ;">??Measurement of the Velocity of Light Between Mount Wilson and Mount San Antonio? , A.A. Michelson, 1927 on page 38 (exhibit) and page 47
John, I'm confused by your referencing the distance from Pasadena East base to Pasadena West base. I don't see why that should be the same as the distance between Michelson and Antonio?
Thanks! Tom
Tom I am having trouble posting. Sometimes it will post and sometimes it won't.
I tried to post another post just after my 1st one but no go.
The distance that Dr. Michelson wanted was from PID EW1861 to PID EV3805 as you posted and that distance using
NGS 27 data is 35,384.7529 mark to mark (I think). We are getting close and I will look for the data tomorrow(I hope).
JOHN NOLTON
Duh, my stupidity scares me sometimes as I have been known to operate heavy machinery. It's been a while since I reviewed all the documentation, but in the second reference I listed above, from 1927, there is Appendix III sitting blatantly at its end by William Bowie of the USCGS describing the survey work. Bowie gives the BM to BM airline distance as 35,385.53 meters. I shoulda known this......
Tom
Can you estimate crustal movement from the baseline points or other marks in the area?
Some links:
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1861&apos ;">EW1861 MICHELSON . Has NAD83(1002) cords and NAD27. last NGS recovery 2007
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EV3805&apos ;">EV3805 ANTONIO Has NAD83(1002) cords and NAD27. Last NGS recovery 1950, note in 1961.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1038&apos ;">EW1038 PASADENA WEST BASE Last posted recovery 1961. Has NAD83(1992) cords and NAD27.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EV3083&apos ;">EV3083 PASADENA EAST BASE Has NAD83(2011) GPS data, NAD83(1992) and NAD27. Last NGS recovery 2016, no GC logs.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EV3082&apos ;">EV3082 PASADENA EAST BASE 2 (no GC logs)
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EV3814&apos ;">EV3814 DIMAS Has NAD83(1002) cords and NAD27. last NGS recovery 1923, no geocaching logs.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1035&apos ;">EW1035 JOAQUIN was reset in 1936/1937 carefully preserving vertical and horizontal position. You can get the data sheet by going through the NGS menus and selecting ??INCLUDE DESTROYED MARKS.? It has only a SCALED NAD83 position given there, but has precise NAD27 coordinates under Superseded.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1034&apos ;">EW1034 JOAQUIN RESET Has NAD83(1992) but no NAD27. Last NGS recovery 1967, geocaching has NF. This provides the shift between datums IF you believe reset was accurately in same place.
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1032&apos ;">EW1032 JOAQUIN RM1 destroyed
https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=EW1033&apos ;">EW1033 JOAQUIN RM1 RESET
Bill93 please try to remember the correct spelling of the word "base line" or base-line but not the way you spell it in
your post above.
JOHN NOLTON
Tom ( aka OtherHand) thanks for the 2 links you posted, it saves me much time in looking for them. Not to worry
about overlooking some things it happens to all of us.
On page 13 of your ref. #2 the distance is 35,385.5 m (what type of distance is not stated)
On the last page (22) the sea level distance is given as 35,373.21 and what they refer to as the air-line distance
(chord) is given as 35,385.53
Thanks for jarring some old memories.
JOHN NOLTON
Of course, I meant to type 1992 and not 1002 above.
Thanks for the pointers to HTDP. That looks like it will do what I need. Since there appears to be an accepted value for the light-line distance between the two BMs (AKA chord) in 1923, I just need to compute the distance between the coords I measured at Antonio and the last valid measurement at Michelson after using HTDP to bring them to the same epoch. Does that sound reasonable?
JOHN NOLTON, post: 455065, member: 225 wrote: Bill93 please try to remember the correct spelling of the word "base line" or base-line but not the way you spell it in
your post above.JOHN NOLTON
John,
In checking my ACSM "Definitions" I see base line and baseline but not base-line.
Paul in PA
Paul in PA The spelling of base line (this is the way its spelled in the United States) has 2 different
ways to spell it according to the Oxford English Dictionary; 1. base line 2. base-line
NGS,BLM and other Govt. agency's spell it the #1. way.
Does this help?
JOHN NOLTON
Fascinating concept. The sea level distance, 35,373.21 meters, is the ellipsoidal distance on the Clarke 1866 ellipsoid. This can be duplicated by INVERSE in the NGS Tool Kit. INVERSE3D uses the GRS80 ellipsoid exclusively, so getting a mark-to-mark distance from the NAD27 coordinates requires calculating the x,y, and z coordinates for both points. I got 35,385.543 meters for that distance, one centimeter different from the old published value.
Using the NAD86 (1992) coordinates and the GRS80 ellipsoid gives a mark-to-mark distance of 35,386.452 meters.
Ellipsoid height is problematic in both calculations. NAD27 assumed that the geoid and ellipsoid were the same (actually, close enough so that the difference is negligible), so orthometric heights are the same as ellipsoid heights. The data sheets for the two points do not give ellipsoid heights, so I calculated them as the sum of the orthometric and geoid heights, which may introduce some error.
The evidence seems to show a separation of almost an additional meter from 1922-23 to 1992.
JOHN NOLTON, post: 455150, member: 225 wrote: Paul in PA The spelling of base line (this is the way its spelled in the United States) has 2 different
ways to spell it according to the Oxford English Dictionary; 1. base line 2. base-line
NGS,BLM and other Govt. agency's spell it the #1. way.Does this help?
JOHN NOLTON
OK, so I check the online Oxford English dictionary and it is perfectly happy with baseline. If I type in base-line it takes me to baseline and no other spelling.
So I then type in "base line" and it gives me a perfectly good explanation of base and base only.
I work in a Colonial (English) State, but around here we use American not English dictionaries.
As far as the government goes a "Calibration Base Line" is a very particular animal. But in other documents baseline is freely used.
Paul in PA
Here's a link with some nice pictures of Antonio (EV3805) and some historical pictures of the baseline measurement. Don't know if this is the OP's site or not.
Yep, it's mine. I linked to the main page it in my first post. Deja vu all over again....
Nice site. And a nice problem. Keep us updated.