Elevation angle and phase residuals for single satellite

Slides:



Advertisements
Similar presentations
Cloud Radar in Space: CloudSat While TRMM has been a successful precipitation radar, its dBZ minimum detectable signal does not allow views of light.
Advertisements

Experimental Results from “BigAnt”, a Large Format Antenna for High Quality Geodetic Ground Stations Gerald Mader National Geodetic Survey (NGS) Silver.
BigAnt * Engineering and Experimental Results * Large Format Antenna for High Quality Geodetic Ground Stations Dmitry Tatarnikov 1, Gerald L Mader 2, Andria.
Magnetic Methods (IV) Environmental and Exploration Geophysics I
METO621 Lesson 18. Thermal Emission in the Atmosphere – Treatment of clouds Scattering by cloud particles is usually ignored in the longwave spectrum.
Extraction of atmospheric parameters M. Floyd K. Palamartchouk Massachusetts Institute of Technology Newcastle University GAMIT-GLOBK course University.
any object in space outside of Earth's atmosphere
Atmospheric effect in the solar spectrum
Effects of azimuthal multipath heterogeneity and hardware changes on GPS coordinate time series Sibylle Goebell, Matt King
GAMIT Modeling Aspects Lecture 04 Thomas Herring
GAMIT Modeling Aspects Lecture 04 Thomas Herring
Estimating Atmospheric Water Vapor with Ground-based GPS Lecture 12
Introduction.
Estimating Atmospheric Water Vapor with Ground-based GPS.
Principles of the Global Positioning System Lecture 11 Prof. Thomas Herring Room A;
Earth Science 17.3 Temperature Controls
Modern Navigation Thomas Herring MW 11:00-12:30 Room
Antennas for Emergency Communications
Estimating Heights and Atmospheric Delays “One-sided” geometry increases vertical uncertainties relative to horizontal and makes the vertical more sensitive.
Chapter 8: The future geodetic reference frames Thomas Herring, Hans-Peter Plag, Jim Ray, Zuheir Altamimi.
Antenna Techniques to Optimize Pseudorange Measurements for Ground Based Ranging Sources Jeff Dickman Ohio University Avionics Engineering Center The 29.
IVS GM January 10, 2006 Interaction of Atmosphere Modeling and VLBI Analysis Strategy Arthur Niell MIT Haystack Observatory.
Modern Navigation Thomas Herring
1 SVY 207: Lecture 12 GPS Error Sources: Part 2 –Satellite: ephemeris, clock, S/A, and A/S –Propagation: ionosphere, troposphere, multipath –Receiver:antenna,
January 14, 2003GPS Meteorology Workshop1 Information from a Numerical Weather Model for Improving Atmosphere Delay Estimation in Geodesy Arthur Niell.
Issues in GPS Error Analysis What are the sources of the errors ? How much of the error can we remove by better modeling ? Do we have enough information.
Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Avenue | Cambridge MA V F
Challenges and Opportunities in GPS Vertical Measurements “One-sided” geometry increases vertical uncertainties relative to horizontal (~3:1) so longer.
Short-session Static and Kinematic Processing Short-session static: GAMIT processing, sessions 1-3 hours long Kinematic: TRACK processing, coordinates.
Atmospheric phase correction at the Plateau de Bure interferometer IRAM interferometry school 2006 Aris Karastergiou.
1 Antennas for Emergency Communications. Emergency Antennas VHF / UHF - FM HF – Voice, CW, or Digital 2.
Challenges and Opportunities in GPS Vertical Measurements “One-sided” geometry increases vertical uncertainties relative to horizontal and makes the vertical.
Chalmers University of Technology Site-Dependent Electromagnetic Effects in High-Accuracy Applications of GNSS Jan Johansson and Tong Ning Chalmers University.
Modeling Errors in GPS Vertical Estimates Signal propagation effects –Signal scattering ( antenna phase center/multipath ) –Atmospheric delay ( parameterization,
IGARSS 2011, Vancuver, Canada July 28, of 14 Chalmers University of Technology Monitoring Long Term Variability in the Atmospheric Water Vapor Content.
Sea Ice, Solar Radiation, and SH High-latitude Climate Sensitivity Alex Hall UCLA Department of Atmospheric and Oceanic Sciences SOWG meeting January 13-14,
GPS snow sensing: results from the EarthScope Plate Boundary Observatory Kristine Larson, Felipe Nievinski Department of Aerospace Engineering Sciences.
Seismic phases and earthquake location
Limits of static processing in a dynamic environment Matt King, Newcastle University, UK.
Limits of static processing in a dynamic environment Matt King, Newcastle University, UK.
Vertical loading and atmospheric parameters
Thomas Herring, IERS ACC, MIT
Vertical loading and atmospheric parameters
Geodesy & Crustal Deformation
Principles of the Global Positioning System Lecture 17
Black Star Chart The small brass ring in the middle is the location of the North Star. The “railroad tracks” around the North Star are the positions of.
GPS: Global Positioning System
Chap IV. Fundamentals of Radar Beam propagation
Fundamentals of GPS for high-precision geodesy
Fundamentals of GPS for geodesy
Geodesy & Crustal Deformation
Cloud conditions for low atmospheric electricity during disturbed period after the Fukushima nuclear accident Akiyo Yatagai1, M. Yamauchi2, M. Ishihara3.
Causes of Seasons Earth’s Tilt Parallelism of Earth’s Axis
GG 450 February 19, 2008 Magnetic Anomalies.
Elevation angle and phase residuals for single satellite
Investigation of site-dependent GPS errors and monument stability using a short-baseline network of braced monuments Emma Hill, Jim Davis, Pedro Elosegui,
Overview of sh_gamit / sh_glred processing
Track Output Interpretation
Finding celestial objects in our night sky … … requires knowing celestial coordinates, based on the time of night, and our location Every star, cluster,
Principles of the Global Positioning System Lecture 14
Principles of the Global Positioning System Lecture 11
Tidal Signatures in the Extended Canadian Middle Atmosphere Model
Every star, cluster, nebula, galaxy,
GPS Ionospheric Mapping at Natural Resources Canada
Track Output Interpretation
Challenges of Radio Occultation Data Processing
Mapping Earth’s Surface
Vertical loading and atmospheric parameters
Technician License Course.
General Licensing Class
Presentation transcript:

Elevation angle and phase residuals for single satellite Epochs 20 0 mm -20 To help you visualize the measurements, I’ve shown the phase recorded for a single satellite at a stations after removing everything we know about the propagation medium and the motion of the station wrt the satellites. 30s samples. Overall rms here is .04 cycles, 8 mm in equivalent path length. At for high elevation angles, the rms is about 2 mm; for low elevation angles about 15 mm. Low elevation angles increase both multipathing and atmospheric delays. Note temporal correlations of 10-20 minutes, suggesting that we have oversampled by a factor of 20-40, and that we should expect the formal errors, propagated from the scatter in the phases, to be too small by a factor of 5 or so. These are due to multipathing and variations in water vapor along the path. 1 2 3 4 5 Hours Elevation angle and phase residuals for single satellite

Simple geometry for incidence of a direct and reflected signal The most common and dominant source of high-frequency multipath is reflection from the horizontal surface beneath the antenna. If this surface is far enough away from the antenna (1-2 m) to be outside the fresnel zone (no interaction with the antenna itself), then geometric optics allows us to model the signal well enough to predict the frequency. For an antenna mounted 1-2 m above the surface, the variations will be of the order of minutes, and tend to have low, though still significant correlatations with the signature of the station’s coordinates and the atmopheric delay. Once you get within a half-meter, though, the longer period variations are a real problem. And this is even without taking into account the interaction with the antenna structure. Multipath contributions to observed phase for an antenna at heights (a) 0.15 m, (b) 0.6 m, and (c ) 1 m. [From Elosegui et al, 1995]

Now we’ve taken the phase vs time residuals and projected them onto the sky. Same 12-hr period for the same stations on two successive days. North to the right!! This is the pattern you see on the sky at mid-latitudes and shows a mixture of N-S and E-W motion, with N-S dominating. At the equator, all the satellites move nearly N-S on the sky, and at the poles more E-W. The dominant motion determines whether the N-S or E-W component of the station position is better determined. You see again the largest fluctuations at low elevation angles, and much of this noise repeats from day to day—signal multipathing. Where you see differences, as near 90 degrees between 20-24 hours, the likely cause is water vapor.

Antenna Phase Patterns The first problem we have is that the phase-response pattern of any physical antenna is not spherical. So the effective phase center ---the point to which you want to refer the location of the ground monument---varies as a function of elevation angle, and hence changes if you use a different minimum cutoff—which can happen when you change receivers or cables because of the change in SNR. Sometimes, the patterns also vary with azimuth, as with the Leica and Rascal antennas here, but most of the antennas used for high precision work have symmetric patterns. L1 phase variations for antennas tested by UNAVCO. Zenith values at the center and values for 10 degrees elevation at the edges. 10 deg L1 phase = 5 mm. From Rocken et a. ???? Antenna Phase Patterns

Top: PBO station near Lind, Washington. Bottom: BARD station CMBB at Columbia College, California We now routinely create phase vs elevation plots in all of our processing. Here are two examples from continuous stations used in my processing of this summer’s PNW survey. The top one is a new PBO station in Eastern Washington. Except for the thin rods supporting the antenna, the support and the area around the antenna is “clean”, and the phase pattern quite flat. An older continuous station, mounted on a pillar, I think.

Left: Phase residuals versus elevation for Westford pillar, without (top) and with (bottom) microwave absorber. Right: Change in height estimate as a function of minimum elevation angle of observations; solid line is with the unmodified pillar, dashed with microwave absorber added To see how sensitive this problem can be, I’ll show first the results of a controlled experiment performed by the Harvard GPS group. They noticed a high dependence of their height estimates for the continuous tracker near the Westford VLBI antenna at Haystack, which they hypothesized was from the metal plate imbedded in the concrete of the pillar supporting the antenna. [From Elosequi et al.,1995]

Correlation between estimates of height and zenith delay as function of minimum elevation angle observed (VLBI, from Davis [1986])

The problem with estimating the zenith delay is that it is highly correlated with estimates of the vertical component of position. With VLBI, we can break this correlation somewhat by observing to very low elevation angles, but with GPS we can’t go this low. You can see from this curve that estimating the zenith delay with a cutoff of 15 degrees increases the vertical uncertainty by over a factor of 5. Uncertainty in estimated height as function of minimum elevation angle observed (VLBI, from Davis [1986]; dotted line with no zenith delay estimated)

The atmospheric delay can vary by decimeters, and though the surface pressure provides an adequate calibration of the the gases in hydrostatic equilibrium, there is no reliable and economical way to remove the contribution of water vapor. So we estimate that portion, parameterized by a delay at the zenith and a mapping function that is reliable to 15 degree elevation angle, the usual lower limit for GPS observations. This slide shows the estimates at 2-hr intervals for two stations used in our analysis of PNW data from last summer. GPS adjustments to atmospheric zenith delay for 29 June, 2003; southern Vancouver Island (ALBH) and northern coastal California (ALEN). Estimates at 2-hr intervals.