New tide gauge uses GPS signals to measure sea level change
Hi:
Classical tide gauges measure the height of the water relative to the gauge. But since the gauge is attached to a
tectonic plate it's elevation is changing.
This is one of the problems I have with the claim that sea level is rising at 2mm per year. i.e. how well can they back
out the plate movement in historical tide gauge records?
The new system uses a pair of GPS antennas one pointed up and the other pointed down at the water.
http://www.mynewsdesk.com/uk/chalmers/pressreleases/new-tide-gauge-uses-gps-signals-to-measure-sea-level-change-998041?utm_source=rss&utm_medium=rss&utm_campaign=Subscription&utm_content=pressrelease
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
On 5/27/14, 10:24 AM, Brooke Clarke wrote:
Hi:
Classical tide gauges measure the height of the water relative to the
gauge. But since the gauge is attached to a tectonic plate it's
elevation is changing.
This is one of the problems I have with the claim that sea level is
rising at 2mm per year. i.e. how well can they back out the plate
movement in historical tide gauge records?
Quite well. This is what geodesy specialists (geodesists?) do for a
living. There's guys and gals at JPL who measure the earth's rotational
axis to fractions of a cm and sub microsecond (with a lot of averaging
and accounting for all sorts of error and offset sources)
I would look for instance, at the Topex/Jason things where they
regularly measure sea surface height to mm accuracy (that's how they
infer ocean temperature and El Nino.. warm water floats on top, etc.)
One should also be aware that very precise altimetry has some
constraints on the publishable data. Over small time and geographic
scales one can see things like the wake of a submarine: the
oceanographers call that "noise" that has to be removed: other people
call that "signal".
In any case, I'd believe a general statement of "mm of seal level
change" over a sufficient averaging interval.
What's more important is why it rises (fresh water floats, so if you get
a warm summer that melts lots of ice, you can get a layer of freshwater
on top of the salt water.
Keeping this time nutsy, there is some research on using reflections of
gps signals to distinguish (e.g. you get a big reflection from the
air/water surface, but you get smaller reflections from the fresh/salt
interface, etc.)
It's similar to the things you can do with trying to look for the
complete correlation graph for a GPS signal, rather than just tracking
the biggest peak.
The new system uses a pair of GPS antennas one pointed up and the other
pointed down at the water.
http://www.mynewsdesk.com/uk/chalmers/pressreleases/new-tide-gauge-uses-gps-signals-to-measure-sea-level-change-998041?utm_source=rss&utm_medium=rss&utm_campaign=Subscription&utm_content=pressrelease
On 5/27/14, 10:24 AM, Brooke Clarke wrote:
This is one of the problems I have with the claim that sea level is
rising at 2mm per year. i.e. how well can they back out the plate
movement in historical tide gauge records?
Let's assume they are NOT good at this and are working with factor of
two error. All you need to know to see there is a problem is the
order of magnitude of the trend.
It's like if someone says "the house is on fire. We have to get out"
and then you argue no it's not because you've got the rate of
combustion off by a factor of 2.73. Small factors don't change the
practical result.
2mm/yr is a small and very conservative estimate. A better one that
reflects current conditions is nearly 4mm/yr. But the worry is that
the rate is not constant and there is some positive feedback. That
seems to be the case but it will take 20 years to really know for
sure.
BACK ON TOPIC... What does it take to measure ones distance from the
center of the Earth accurately enough to detect geological movement in
a reasonable amount of time? Measuring distance really is, I think
a time nut problem as I bet it involves measuring radio waves.
Chris Albertson
Redondo Beach, California
Which begs the question: just where the heck, exactly, is the center of the
Earth given that it is in the 'middle' of a molten and dynamic core. Are the
satellite orbits so stable and/or measurable around the center of
gravitational pull that the location can be determined from that? Where is
the reference point? Is Archimedes fulcrum for moving the planet nearby?
This would seem to play into the accuracy of the location of the GPS
satellites at any given time-hack.
Tom Holmes, N8ZM
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chris Albertson
Sent: Wednesday, May 28, 2014 12:22 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] New tide gauge uses GPS signals to measure sea
level change
On 5/27/14, 10:24 AM, Brooke Clarke wrote:
This is one of the problems I have with the claim that sea level is
rising at 2mm per year. i.e. how well can they back out the plate
movement in historical tide gauge records?
Let's assume they are NOT good at this and are working with factor of
two error. All you need to know to see there is a problem is the
order of magnitude of the trend.
It's like if someone says "the house is on fire. We have to get out"
and then you argue no it's not because you've got the rate of
combustion off by a factor of 2.73. Small factors don't change the
practical result.
2mm/yr is a small and very conservative estimate. A better one that
reflects current conditions is nearly 4mm/yr. But the worry is that
the rate is not constant and there is some positive feedback. That
seems to be the case but it will take 20 years to really know for
sure.
BACK ON TOPIC... What does it take to measure ones distance from the
center of the Earth accurately enough to detect geological movement in
a reasonable amount of time? Measuring distance really is, I think
a time nut problem as I bet it involves measuring radio waves.
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 5/27/14, 9:21 PM, Chris Albertson wrote:
On 5/27/14, 10:24 AM, Brooke Clarke wrote:
BACK ON TOPIC... What does it take to measure ones distance from the
center of the Earth accurately enough to detect geological movement in
a reasonable amount of time? Measuring distance really is, I think
a time nut problem as I bet it involves measuring radio waves.
Considering that the Pacific Plate is moving north at about 2cm/year,
that is easily detectable with GPS and post processing. Somebody in
Southern California should be able to measure it without going to too
exotic an effort: you need a GPS receiver that can put out the
observables in a gipsy file, and then post process through JPL's website.
The Ventura Anticline is still rising at about the same rate.
On 5/28/14, 6:04 AM, Tom Holmes wrote:
Which begs the question: just where the heck, exactly, is the center of the
Earth given that it is in the 'middle' of a molten and dynamic core. Are the
satellite orbits so stable and/or measurable around the center of
gravitational pull that the location can be determined from that? Where is
the reference point? Is Archimedes fulcrum for moving the planet nearby?
This would seem to play into the accuracy of the location of the GPS
satellites at any given time-hack.
T
There's a group of people around the world who worry about this kind of
thing. There's a difference between the barycenter (the "center of
mass") and the Earth centered coordinate system orgins. In fact, there's
somewhat of a dispute going on about whether we should update from
WGS84: that coordinate system was defined to be the same (within
measurement precision) as the previous origin, but now "within
measurement precision" has gotten smaller, and there's a difference.
But that raises a question of whether we need to redo all the state
plane coordinate transformations, since they're in terms of WGS84.
As to whether the satellite orbits are stable/measurable, the answer is
most certainly yes. It was fairly precise measurements of satellite
signals in the 60s that led to the changing of the geoid from an
ellipsoid to something more "pear" shaped.
Precise measurements of satellite orbits and Doppler rates is how we
infer the internal structure of the outer planets. A typical
measurement uncertainty is a few cm and a few mm/sec for a probe at
Jupiter.
One generally does some sort of fit to a gravitational model with some
number of spherical harmonic terms (ten or twenty, as I recall).
The ephemeris for GPS takes this into account, so if you also account
for things like the ionosphere, you can determine your position to cm
accuracy (absolute). Note well that the GPS ephemeris doesn't contain
all the spherical harmonics and effects.. what they do is reload the
ephemeris periodically with fewer terms so that you can use it for a few
days (as I recall, for satelites in "reasonable" orbits (not too low),
the uncertainty in satellite position after a day is on the order of
meters.
Some satellites are particularly stable: QuikScat was in a special
orbit, and as I recall, after a year, it was only a few hundred meters
from where the year old ephemeris predicted it would be. The orbit
height (803 km) had changed maybe 1 km.
Thanks Jim.
So if, just for fun since this is time-nuts after all, I wanted to make a
similar measurement in my back yard here in the relatively stable Ohio,
would I be able rig something up to monitor the position changes? Obviously
a lot of averaging of GPS position data would be needed but I'm not sure my
Z3801 or any of my navigation receivers have the necessary resolution to see
even 10 mm.
Tom Holmes, N8ZM
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Jim Lux
Sent: Wednesday, May 28, 2014 4:54 PM
To: time-nuts@febo.com
Subject: Re: [time-nuts] New tide gauge uses GPS signals to measure sea
level change
On 5/28/14, 6:04 AM, Tom Holmes wrote:
Which begs the question: just where the heck, exactly, is the center of
the
Earth given that it is in the 'middle' of a molten and dynamic core. Are
the
satellite orbits so stable and/or measurable around the center of
gravitational pull that the location can be determined from that? Where is
the reference point? Is Archimedes fulcrum for moving the planet nearby?
This would seem to play into the accuracy of the location of the GPS
satellites at any given time-hack.
T
There's a group of people around the world who worry about this kind of
thing. There's a difference between the barycenter (the "center of
mass") and the Earth centered coordinate system orgins. In fact, there's
somewhat of a dispute going on about whether we should update from
WGS84: that coordinate system was defined to be the same (within
measurement precision) as the previous origin, but now "within
measurement precision" has gotten smaller, and there's a difference.
But that raises a question of whether we need to redo all the state
plane coordinate transformations, since they're in terms of WGS84.
As to whether the satellite orbits are stable/measurable, the answer is
most certainly yes. It was fairly precise measurements of satellite
signals in the 60s that led to the changing of the geoid from an
ellipsoid to something more "pear" shaped.
Precise measurements of satellite orbits and Doppler rates is how we
infer the internal structure of the outer planets. A typical
measurement uncertainty is a few cm and a few mm/sec for a probe at
Jupiter.
One generally does some sort of fit to a gravitational model with some
number of spherical harmonic terms (ten or twenty, as I recall).
The ephemeris for GPS takes this into account, so if you also account
for things like the ionosphere, you can determine your position to cm
accuracy (absolute). Note well that the GPS ephemeris doesn't contain
all the spherical harmonics and effects.. what they do is reload the
ephemeris periodically with fewer terms so that you can use it for a few
days (as I recall, for satelites in "reasonable" orbits (not too low),
the uncertainty in satellite position after a day is on the order of
meters.
Some satellites are particularly stable: QuikScat was in a special
orbit, and as I recall, after a year, it was only a few hundred meters
from where the year old ephemeris predicted it would be. The orbit
height (803 km) had changed maybe 1 km.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 5/28/14, 2:11 PM, Tom Holmes wrote:
Thanks Jim.
So if, just for fun since this is time-nuts after all, I wanted to make a
similar measurement in my back yard here in the relatively stable Ohio,
would I be able rig something up to monitor the position changes? Obviously
a lot of averaging of GPS position data would be needed but I'm not sure my
Z3801 or any of my navigation receivers have the necessary resolution to see
even 10 mm.
T
Sure it can.. you don't do it by averaging lat/lons, though...
What you need is to program your receiver to give you the raw
observables (someone on the list can point you to how you do this), and
then you need to get them in what's called RINEX file format. You
submit your RINEX formatted files to JPL's web based GIPSY processing
site (wait at least a week or two after you collect your data, so they
have the precise GPS ephemeris figured out), and get your geodetic data
back.
As I recall, given your position, they have post hoc ionospheric
calculations from recordings made at high precision receivers near you
which they can use to compensate your measurements, etc.
I'm oversimplifying a lot of the above process out of ignorance, but
basically that's how it's done.
I have been told that it's pretty easy to see things like solid earth
tides with a fairly simple system. Mind you "fairly simple" to these
guys might mean a high quality choke ring on a geodetic pedestal with a
precision invar rod driven into the bedrock within a steel protective
casing. but it could also mean a helibowl antenna with the helix wound
on a plastic solo cup stuck inside an aluminum kitchen stove burner liner.
One of the longest continuously running geodetic receiver stations is at
JPL and is basically a D&M choke ring sitting on the ground on the edge
of a hill. (this is referred to as the Aries Site*, for some reason)
in the lower right corner of the dirt area south of the parking lot
area, you'll see a dark dot in the middle of a lighter round thing:
that's the antenna.
The trailer at the top of the image is where the receiver is, and the
coax is running along the east side of the parking lot.
Contrary to the copyright date at the bottom, this image is at least 2
years old, because they've moved the trailer away, and the receiver is
now in a little building across the street (on the west side of the image).
*It might well be that initial testing of ARIES (a VLBI experiment)
http://ipnpr.jpl.nasa.gov/progress_report2/42-26/26G.PDF
was done up there. There's a couple surveyed concrete pads with steel
mounts and benchmarks. The DSN report was from 1975, so it's
substantially before my time at the lab (as well as most people around),
although there are some familiar names in that paper (Spitzmesser has
dozens of GPS related pubs)
https://ia600505.us.archive.org/3/items/nasa_techdoc_19840071052/19840071052.pdf
has a picture of the smaller 4 meter system (it's more portable than the
9 meter system, and claims better performance because of the liquid
helium cooled maser, portable cesium clock, etc.) I guess "portable" is
relative, especially when you talk to DSN folks who think in terms of 70
meter antennas. (For scale..the building in the background of the
picture is Bldg 180 at JPL, the main admin building, and is 9 stories
tall. A 70 meter DSN antenna is taller than that building)
what's fascinating is that today, you can buy, for less than $20, a low
noise block converter for 12 GHz (Ku-band) with a noise temperature <20K.
But back in the early 70s, "pre-GPS" days, you had to be a serious
time-nut...
On Wed, May 28, 2014 at 6:28 PM, Jim Lux jimlux@earthlink.net wrote:
What you need is to program your receiver to give you the raw observables
(someone on the list can point you to how you do this), and then you need
to get them in what's called RINEX file format. You submit your RINEX
formatted files to JPL's web based GIPSY processing site (wait at least a
week or two after you collect your data, so they have the precise GPS
ephemeris figured out), and get your geodetic data back.
The JPL system says it will do single frequency in the future so for now I
think you need a dual frequency(L1/L2) receiver. The Canadian Geomatics
group does single frequency and of course you can do your own
post-processing. RTKLIB (I think first mentioned here in 2011) seems to be
popular. PPP is why I have LEA-6T and NEO-7P receivers.
RTKLIB says it can locate my antenna within a 2x5x10 cm volume given a few
days of data.
On 28 May 2014 14:06, "Tom Holmes" tholmes@woh.rr.com wrote:
Which begs the question: just where the heck, exactly, is the center of
the
Earth given that it is in the 'middle' of a molten and dynamic core.
I always thought that the centre was molten. There was something on the TV
in the UK a couple of weeks ago which seemed to indicate that the centre is
actually solid, although around that it is molten.
I did not see it all and was only watching bits of it, but it would appear
some female researcher had proven this. The proof appeared to be based on
the time of travel of shock wases from earthquakes and the different speed
they travel through solid and liquid.
Dave.