Earth Remote Sensing with Earth Remote Sensing with Satellite Navigation SignalsSatellite Navigation Signals

IEEC Current projectsIEEC Current projects

A. RiusA. RiusIEEC, September 2004IEEC, September 2004

Earth Science and Technology Earth Science and Technology DepartmentDepartment

Antonio RiusAntonio Rius Pedro EloseguiPedro Elosegui Oleguer NoguesOleguer Nogues Serni RibóSerni Ribó Josep SanzJosep Sanz Txepo Torrobella BadíaTxepo Torrobella Badía Myrthe BeekhuisMyrthe Beekhuis Santi OliverasSanti Oliveras Benji GarzonBenji GarzonConsultoresConsultores Josep Maria Aparicio, Inst. Met CanadaJosep Maria Aparicio, Inst. Met Canada Estel Cardellach, CfA. Enero 2005 de la CiervaEstel Cardellach, CfA. Enero 2005 de la Cierva

Occultations

TransmitterReceiver

Refractivity gradient

Beam of rays

Reflections

Transmitter (GPS (DOD) or Radio Source (GOD) or RADAR)

Receiver (space, aircraft, ground......)

Planet, satellite,

2*h*

sin(

el)

el2*h

Direct signal Reflected signal

Specular point

Receiver direct

Transmitter

Receiver reflected

Doppler Delay mapping

Scattering (nadir case)

Scattering (oblique case)

88

Geodetic TechniquesGeodetic Techniques

Space Geodetic and related Techniques at Space Geodetic and related Techniques at microwave frequencies:microwave frequencies: Very Long Baseline InterferometryVery Long Baseline Interferometry Global Positioning System Global Positioning System Other GNSSOther GNSS Radar altimetersRadar altimeters

The observables are differences in the arrival The observables are differences in the arrival epochs of microwave signals. These differences epochs of microwave signals. These differences are affected by the atmospheric refractivity or the are affected by the atmospheric refractivity or the surface scattering properties. surface scattering properties.

Global Navigation Satellite Global Navigation Satellite SystemsSystems

Global Positioning System (GPS/USA) [24]Global Positioning System (GPS/USA) [24] GLObal’naya Navigatsionnaya Sputnikova GLObal’naya Navigatsionnaya Sputnikova

Sistema (GLONASS/ Russia) [24]Sistema (GLONASS/ Russia) [24] future GALILEO? (EU) [30]future GALILEO? (EU) [30] Communication Satellites: Communication Satellites: Inmarsat [4], Artemis [1]Inmarsat [4], Artemis [1]

Potentially, 50-80 satellites freelytransmitting L-band coded signal

1010

ResourcesResources 24 operational satellites at an altitude of 20,000 24 operational satellites at an altitude of 20,000

km.km. Transmit ranging data (1.2 and 1.6 GHz) to Transmit ranging data (1.2 and 1.6 GHz) to

ground-basedground-based receivers. receivers. The GPS system measures time delays between The GPS system measures time delays between

the transmission and reception of the the transmission and reception of the electromagnetic signals.electromagnetic signals.

These delays contain information on the distance These delays contain information on the distance between satellites and receivers: geometric delay.between satellites and receivers: geometric delay.

Delays are also affected by the presence of matter Delays are also affected by the presence of matter along the path: atmospheric delay (ionosphere and along the path: atmospheric delay (ionosphere and troposphere) gravitational delay.troposphere) gravitational delay.

the atmosphere affects the signal propagationthe atmosphere affects the signal propagation extra delayextra delay (slowing effect) (slowing effect) curved path (bending effect)curved path (bending effect) GPS MeteorologyGPS Meteorology

The sea surface is a good conductor at L Band. The sea surface is a good conductor at L Band. The signal could be reflected on the sea surface or The signal could be reflected on the sea surface or ice, snow,.... ice, snow,.... GPS Oceanography GPS Oceanography

Global Navigation Satellite Global Navigation Satellite Systems: GPS signalSystems: GPS signal

Global Navigation Satellite Global Navigation Satellite Systems: GPS signalSystems: GPS signal

2 carriers, common to all transmitters: 2 carriers, common to all transmitters: L1=1.575 GHz L2=1.228 GHzL1=1.575 GHz L2=1.228 GHz

Code Division Multiple Access: phase Code Division Multiple Access: phase modulation by orthogonal Pseudo-modulation by orthogonal Pseudo-Random Noise, characteristic of each Random Noise, characteristic of each transmitter.transmitter.

Current PRN-Codes:Current PRN-Codes:– C/A coarse, 300m, P=1ms (L1)C/A coarse, 300m, P=1ms (L1)

– P precise, 30m, P=1week, encryptedP precise, 30m, P=1week, encrypted Navigation message: 50bpsNavigation message: 50bps

1313

IGS NetworkIGS Network

ObjectivesObjectives

Space Geodetic Techniques objectivesSpace Geodetic Techniques objectivesTo provide coordinates to points (position and To provide coordinates to points (position and

time) in well defined reference framestime) in well defined reference framesThe receivers are placed in moving platforms :The receivers are placed in moving platforms :

Earth crust (cm/year)Earth crust (cm/year)LEOsLEOsAirplanesAirplanesSea buoysSea buoysBalloons (wind speed radiosondes)Balloons (wind speed radiosondes)

The signal path could be:The signal path could be: “ “deterministic” or “random”deterministic” or “random”Direct or after reflectionDirect or after reflection

MeasurementsMeasurements

Space Geodetic Techniques: MeasurementsSpace Geodetic Techniques: Measurements Phase and group Delays experienced by EM signals from Phase and group Delays experienced by EM signals from

transmitter to receiver antennas.transmitter to receiver antennas. The precision of the phase measurements is below 1 mm after 1 The precision of the phase measurements is below 1 mm after 1

second of integration. second of integration. The accuracy is in the order of 1 meter for the group delays The accuracy is in the order of 1 meter for the group delays

(pseudoranges) (pseudoranges)

Delays depends on Delays depends on The physical structure of the antennasThe physical structure of the antennas The geometry and dynamics of the antennasThe geometry and dynamics of the antennas The path followed by the signalThe path followed by the signal The EM properties of the medium traversing the signal The EM properties of the medium traversing the signal Instrumental errors in the receivers and in the transmittersInstrumental errors in the receivers and in the transmitters

AnalysisAnalysis

Space Geodetic Techniques: AnalysisSpace Geodetic Techniques: Analysis The measurements are analyzed with a (simplified) model, The measurements are analyzed with a (simplified) model,

defined trough a set of stochastic processesdefined trough a set of stochastic processes Receiver coordinates (including geophysical phenomena)Receiver coordinates (including geophysical phenomena) Transmitter coordinates (including phenomena perturbing the orbits)Transmitter coordinates (including phenomena perturbing the orbits) Ionosphere and troposphere refractivityIonosphere and troposphere refractivity Antenna phase patternsAntenna phase patterns Instrumental biasesInstrumental biases

Because the correlations among the stochastic processes it is not Because the correlations among the stochastic processes it is not possible to solve for everything. possible to solve for everything.

The selection of the processes to estimate depends on the The selection of the processes to estimate depends on the application.application.

ResultsResults

Space Geodetic Techniques: Results (typical)Space Geodetic Techniques: Results (typical) Typical precisions of the estimations are:Typical precisions of the estimations are:

5 mm for the receiver coordinates5 mm for the receiver coordinates5 cm for the transmitter coordinates5 cm for the transmitter coordinates1 cm for the zenith tropospheric delay1 cm for the zenith tropospheric delay

Below these quantitities the system is Below these quantitities the system is controled by coloured noisecontroled by coloured noise

One man’s trash is another man’s treasureOne man’s trash is another man’s treasure One man’s signal is another man’s noiseOne man’s signal is another man’s noise

High accuracy High accuracy

geodeticgeodeticsystemssystems

ZTD, WZDZTD, WZDIWVIWVMultipathMultipathScatteringScattering

Nuisance parameters

NWP models,NWP models,Ocean modelsOcean models

The tropospheric delayThe tropospheric delay

Observed delayObserved delay = = geometrical delay + ionospheric delay + geometrical delay + ionospheric delay + tropospheric delay + instrumental delaytropospheric delay + instrumental delay

The geometrical delay can be computed from the positions of the transmitter and the receiver. The position can be modeled with geophysical information which accounts for Earth tides, ocean loading, etc.The ionospheric delay depends on the frequency and can be removed using two different frequencies.Instrumental effects are essentially time independent (scale of minutes).Observed delay – corrections = Observed delay – corrections = tropospheric delaytropospheric delay

But, notice that with this definition the tropospheric delay are “correlated measures”

WV is a small fraction of atmospheric gases WV is a small fraction of atmospheric gases (fractional volume 0 - 4 %).(fractional volume 0 - 4 %). Distribution and content are critical for the Distribution and content are critical for the

description of the state and evolution of the description of the state and evolution of the atmosphere.atmosphere.

Highly variable in time and space and correlates Highly variable in time and space and correlates poorly with surface humidity measurements.poorly with surface humidity measurements.

Lack of precise and continuous WV data is one of Lack of precise and continuous WV data is one of the major error sources in short-term forecasts of the major error sources in short-term forecasts of precipitation (Kuo et al. 1993, 1996).precipitation (Kuo et al. 1993, 1996).

Current observational techniques:Current observational techniques:radiosondes (expensive, poor temporal radiosondes (expensive, poor temporal

resolution, poor spatial coverage)resolution, poor spatial coverage)ground-based and space-based WVR ground-based and space-based WVR

(poor spatial coverage or poor temporal (poor spatial coverage or poor temporal resolution, expensive).resolution, expensive).

A new observational technique A new observational technique ((Bevis et Bevis et

al. 1992):al. 1992): GPS systemGPS system precise and continuous estimates ofprecise and continuous estimates of WVWV

The tropospheric delay of the GPS signal is the integral of The tropospheric delay of the GPS signal is the integral of the refractivity N along the ray path. the refractivity N along the ray path.

Neglecting liquid water contribution and ionospheric effects Neglecting liquid water contribution and ionospheric effects (Smith and Weintraub 1953),(Smith and Weintraub 1953),

Slant Troposheric delay Slant Troposheric delay Zenith Tropospheric Delay (ZTD)Zenith Tropospheric Delay (ZTD) ZTD is estimated with a formal error of ZTD is estimated with a formal error of 5 mm5 mm (Businger et al. 1996) at (Businger et al. 1996) at

around around 10-min10-min interval. interval.

2321 NT

Pk

T

Pk

T

Pk wwd

wet chydrostati N N N

Zenith Hydrostatic delayZenith Hydrostatic delay (ZHD)(ZHD) typical value of typical value of 2300 mm2300 mm at sea level. at sea level. accurately modeled if measurements of surface accurately modeled if measurements of surface

pressure (barometer or a NWP model) are pressure (barometer or a NWP model) are

available (Saastamoinen 1972).available (Saastamoinen 1972). error of 0.4 mb in Perror of 0.4 mb in Pss less than 1 mm error of ZHD less than 1 mm error of ZHD

GPS Radio OccultationGPS Radio Occultation The 24 GPS satellites are The 24 GPS satellites are

distributed roughly in six circular distributed roughly in six circular orbital planes at ~55orbital planes at ~55o o inclination, inclination, 20,200 km altitude and ~12 hour 20,200 km altitude and ~12 hour periods.periods.

Each GPS satellite continuously Each GPS satellite continuously transmits signals at two L-band transmits signals at two L-band frequencies, L1 at 1.57542 GHz frequencies, L1 at 1.57542 GHz (~19 cm) and L2 at 1.227 GHz (~19 cm) and L2 at 1.227 GHz (~24.4 cm).(~24.4 cm).

A ray passing through the A ray passing through the atmosphere is refracted due to atmosphere is refracted due to the vertical gradient of density.the vertical gradient of density.

GPSsatellite

Low Earth Orbiting(LEO) satellite

Future GPS Occultation Missions Future GPS Occultation Missions

METOPMETOP

Metop is the European component of the joint Europe/US polar satellite systemIt will have a GPS receiver for occultations.

Future GPS Occultation Missions Future GPS Occultation Missions

COSMICIt is planned to be

launched in spring 2005

1) Six spacecraft2) GPS receiver

GPS OccultationGPS OccultationUsed to probe planetary atmospheres (1970-...)The bending of the radio path provides information on thevertical distribution of the refractivityThe bending produces an additional (and measurable) doppler shift in the signal

GPS made possible to apply the technique to the Earth.It provides vertical resolution better than 1 km.

Occulting LEOEarth

Troposphera

Ionosphera

Occultations vs. Radio SondesOccultations vs. Radio Sondes

Metop will use a GPS fiducial network. Metop will need to estimate orbits, satellite clocks, etc as in ground based GPS meteorology

The GRAS Ground segment has resources useful for ground GPS meteorology

Synergy

Usual approachesUsual approaches

In general, a key ingredient is to use linear In general, a key ingredient is to use linear algorithms as much as possiblealgorithms as much as possible

Robustness: Non-linear algorithms risk to be Robustness: Non-linear algorithms risk to be unstable, non convergent...unstable, non convergent...Speed: Processing time for linear algorithms Speed: Processing time for linear algorithms is predictable, and in general small.is predictable, and in general small.Accuracy: Allowing non linearity is usually in Accuracy: Allowing non linearity is usually in advantage. A broader class can be used.advantage. A broader class can be used.

First approaches to occultation First approaches to occultation processingprocessing

Simple and fast algorithms exist:Simple and fast algorithms exist:– Doppler evaluationDoppler evaluation– Bending angles & impact parametersBending angles & impact parameters– Abel transformAbel transform

This solves the problem of extracting This solves the problem of extracting some quick solutionsome quick solution

However:However:– Not very accurateNot very accurate– Algorithmically weak against cycle slipAlgorithmically weak against cycle slip– Unable to process open loop dataUnable to process open loop data

Some reflections before Some reflections before proceedingproceeding

What is missing in the Abel approach?What is missing in the Abel approach?– We are actually extracting the atmospheric We are actually extracting the atmospheric

structure from scratch at every profilestructure from scratch at every profile– In early radiooccultations (Venus, Mars), this In early radiooccultations (Venus, Mars), this

was necessary: the target was the climatic was necessary: the target was the climatic profileprofile

– But we are looking here for the meteorological But we are looking here for the meteorological info: i.e. the departure from the climatic profileinfo: i.e. the departure from the climatic profile

Hint:Hint:

At the surface: NAt the surface: N≈≈300300±±30 (about 10% is unknown to us in advance)30 (about 10% is unknown to us in advance)

At 16 km: NAt 16 km: N≈≈3030±1.5±1.5 (only 5% is unknown to us in advance) (only 5% is unknown to us in advance)

We are loosing opportunities if we do not use this informationWe are loosing opportunities if we do not use this information

Subtraction of known Subtraction of known informationinformation

It is standard to It is standard to subtract vacuum-subtract vacuum-propagated values of propagated values of phase, Doppler, etc.phase, Doppler, etc.

But we know enough But we know enough about the Earth's about the Earth's atmosphere to be atmosphere to be able to subtract the able to subtract the climatic component.climatic component.

The residual is much The residual is much smaller.smaller.

Climatic subtraction issues IClimatic subtraction issues I

The climatic subtraction requires a raytracing The climatic subtraction requires a raytracing (comparatively expensive and risky)(comparatively expensive and risky)

However:However: Unlike gridded ones, the climatic model tested Unlike gridded ones, the climatic model tested

(MSISE) is sufficiently well behaved for the (MSISE) is sufficiently well behaved for the raytracing to predictably converge and succeedraytracing to predictably converge and succeed

Not all samples need to be traced. Smoothness Not all samples need to be traced. Smoothness of the climatic model allows raytracing at 1-2 Hz, of the climatic model allows raytracing at 1-2 Hz, which can be interpolated to the typical sampling which can be interpolated to the typical sampling rates (ranging 50-1000 Hz)rates (ranging 50-1000 Hz)

Climatic subtraction issues IIClimatic subtraction issues II

Atmospheric radius of curvature depends Atmospheric radius of curvature depends on the direction, and even changes on the direction, and even changes during an occultationduring an occultation

Algorithms based on spherical symmetry Algorithms based on spherical symmetry are contaminated by this (not only by are contaminated by this (not only by horizontal gradients!)horizontal gradients!)

Most of the contamination from the Most of the contamination from the ellipsoidal shape and variable curvature ellipsoidal shape and variable curvature is removed with climatic raytracingis removed with climatic raytracing

Zenith Wet delayZenith Wet delay (ZWD)(ZWD)

smaller value (0-300 mm)smaller value (0-300 mm) very difficult to model: highly variable in space and time.very difficult to model: highly variable in space and time. associated with Precipitable Water (PW).associated with Precipitable Water (PW). If surface pressure measurements are available, If surface pressure measurements are available, ZWDZWD = ZTD - ZHD = ZTD - ZHD ~~ 6.6 PW6.6 PW

PW can be retrievedPW can be retrieved with a rms error of with a rms error of around around 1 mm1 mm (Herring 1990, Rocken et al. 1997).(Herring 1990, Rocken et al. 1997).

MotivationMotivation

GNSSGNSS: : GGlobal lobal NNavigation avigation SSatellite atellite SSystemystem– Compound by a large Compound by a large

constellation of satellites, constellation of satellites, transmitting coded signalstransmitting coded signals

– Direct reception by the user Direct reception by the user (ground, aircraft, spacecraft) (ground, aircraft, spacecraft) for positioning purposes.for positioning purposes.

Motivation: GNSS reflection Motivation: GNSS reflection conceptconcept

Main advantages of Main advantages of the GNSSr concept: the GNSSr concept:

– FREE SIGNALS, ALREADY EXIST FREE SIGNALS, ALREADY EXIST – PASSIVEPASSIVE– MULTISTATIC MULTISTATIC

Sea level, SWH, roughness/windsalinity, ice, oil...

Tropospheric delay

1993: [1993: [Martín-NeiraMartín-Neira] proposes the ] proposes the PARIS concept: PAssive Reflectometry PARIS concept: PAssive Reflectometry and Interferometry System.and Interferometry System.

1998: studies of GPSr for altimetry and 1998: studies of GPSr for altimetry and sea surface topography. sea surface topography.

1956 : radiosources observed with sea interferometer1956 : radiosources observed with sea interferometer Radar astronomy (meteorites also!)Radar astronomy (meteorites also!) 1970: [1970: [Peterson et al.Peterson et al.] proved the sensitivity of bistatic radar at ] proved the sensitivity of bistatic radar at

radiowaves from ground-based stations.radiowaves from ground-based stations.

The PARIS conceptThe PARIS concept

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

Dielectric proprieties Dielectric proprieties of the sea water: of the sea water: capacity to reflect L-capacity to reflect L-band signals.band signals.

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

Each point on the sea surface has certain Each point on the sea surface has certain capability to forward the incoming signal in the capability to forward the incoming signal in the direction of the receiver:direction of the receiver: scattering coefficientscattering coefficient 00

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

Mean Square Slope (mss) is the Mean Square Slope (mss) is the parameter accounting for the sea parameter accounting for the sea roughness, linked to the wind through roughness, linked to the wind through different models (different models (ElfouhailyElfouhaily, , ApelApel,…),…)

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

BUT: BUT: the signals reflected from different points on the sea the signals reflected from different points on the sea surface have different surface have different relative delayrelative delay..

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

MOREOVER: MOREOVER: the signals reflected from different the signals reflected from different points on the sea surface have different points on the sea surface have different Doppler Doppler frequency offsetfrequency offset..

It is possible, thus, to It is possible, thus, to MAPMAP the illuminated area by the illuminated area by correlating the signal with replicas of the code at correlating the signal with replicas of the code at different different DELAY DELAY lags and lags and DOPPLERDOPPLER frequencies. frequencies.

Modelling the GNSS reflected Modelling the GNSS reflected signalsignal

Hence, the squared correlation function for Hence, the squared correlation function for different delay-Doppler lags (waveform) different delay-Doppler lags (waveform) contains information about the distribution of contains information about the distribution of the reflected power along the sea surfacethe reflected power along the sea surface

System AnalysisSystem Analysis

Aircraft (10km): wind vector retrieval better Aircraft (10km): wind vector retrieval better than [1 m/s,15deg] up to 17 m/sthan [1 m/s,15deg] up to 17 m/s

LEO (350km): wind speed retrieval better LEO (350km): wind speed retrieval better than 2 m/s up to 15 m/s. The direction can than 2 m/s up to 15 m/s. The direction can be inferred (<30deg) using 100 chips of the be inferred (<30deg) using 100 chips of the waveform:waveform:– Low spatial resolutionLow spatial resolution– instrumental drawbacksinstrumental drawbacks New inversion

techniques

QUESTION-1, SUMMARY:QUESTION-1, SUMMARY:

System AnalysisSystem Analysis

QUESTION-2: coverage from spaceQUESTION-2: coverage from space Tool: specular locator [Tool: specular locator [Aparicio et al., 2000Aparicio et al., 2000], ],

given a GPS orbits file and the LEO/s given a GPS orbits file and the LEO/s parameters, it computes the location of the parameters, it computes the location of the specular reflection points and informs about specular reflection points and informs about its geometry (elevation, receiver off nadir its geometry (elevation, receiver off nadir angle...)angle...)

Cases: Cases: 1LEO; 3LEO-1PLANE; 3LEO-3PLANES1LEO; 3LEO-1PLANE; 3LEO-3PLANES polar polar orbits, at 350-400 km altitude.orbits, at 350-400 km altitude.

System AnalysisSystem Analysis

1LEO (350-400km): good coverage, near the 1LEO (350-400km): good coverage, near the User Requirements (UR). Global User Requirements (UR). Global representation in 12 h. UR binning time: 72h.representation in 12 h. UR binning time: 72h.

3LEOs-1PLANE: UR binning time and Global 3LEOs-1PLANE: UR binning time and Global representation: 12 h.representation: 12 h.

3LEOs-3PLANES: UR binning time in 24 h. 3LEOs-3PLANES: UR binning time in 24 h. Global representation: 4 h.Global representation: 4 h.

Multistatic character yields useful coverage

QUESTION-2, SUMMARY:QUESTION-2, SUMMARY:

Experimental workExperimental work

– ESTEC/IEEC/Repsol collaboration. ESTEC/IEEC/Repsol collaboration. Validation of the delay-Doppler software Validation of the delay-Doppler software pre-processor. 20.5MHz raw datapre-processor. 20.5MHz raw data

– NASA/IEEC/ASI/INTA collaboration. Delay-NASA/IEEC/ASI/INTA collaboration. Delay-map Hardware receiver on board a map Hardware receiver on board a stratospheric balloon. 1 Hz Delay-stratospheric balloon. 1 Hz Delay-waveforms.waveforms.

CASABLANCACASABLANCA

MEBEXMEBEX

Experimental work: Experimental work: CASABLANCACASABLANCA

Experimental work: Experimental work: MEMEditerranean diterranean BBalloon alloon

EXEXperimentperiment

Experiment overview:Experiment overview:

Bistatic Altimetry:Bistatic Altimetry:

Determination of relative delays Determination of relative delays for altimetryfor altimetry

Doppler mapping for Doppler mapping for scatterometry:scatterometry:

Processed dataProcessed data

The data is stored in The data is stored in a 3D grid:a 3D grid:– delay lagdelay lag– frequency offsetfrequency offset– timetime

Visualisation with Visualisation with vis5dvis5d

GPS antennas at seaGPS antennas at sea

Reference station Reference station (to estimate tropospheric delays)(to estimate tropospheric delays)

Mapping the sea surface Mapping the sea surface using buoys equipped with using buoys equipped with GPS receiversGPS receiversThe straight line is the T/P subtrack The straight line is the T/P subtrack pathpathAt the points A, B, C, D, E, H, I the At the points A, B, C, D, E, H, I the buoys collected data for one hour. At buoys collected data for one hour. At point O data was collected permanently point O data was collected permanently to monitor systematic variations of the to monitor systematic variations of the sea levelsea level

Comparison Comparison Topex/Poseidon Topex/Poseidon vs GPS buoysvs GPS buoys The green The green crosses are GPS crosses are GPS estimates at the estimates at the points along the points along the T/P trackT/P trackThe blue points The blue points are T/P mean are T/P mean sea level values sea level values

Glistening surfaceGlistening surface

Filters in the radar equationFilters in the radar equation

Delay-Doppler MappingDelay-Doppler MappingEach point in the sea surface could be clasified according to:a) Is inside the glistening surface?b) Its isodelay-isodoppler coordinatesNote that there are ambiguitiesThe observable is the power detected as a function of the iso-delay and the iso-doppler coordinates

Comparison Comparison Topex/Poseidon Topex/Poseidon vs GPS buoysvs GPS buoys The green The green crosses are GPS crosses are GPS estimates at the estimates at the points along the points along the T/P trackT/P trackThe blue points The blue points are T/P mean are T/P mean sea level values sea level values

GOLD-RTR

The IEEC’s aircraft sensor based on the PARIS concept

Authors:•Toni Rius (Project Manager)

•Josep Sanz (Instrument Software Developer Engineer)•Josep Torrobella (Hardware Engineer)

•Oleguer Nogués (System and Hardware Engineer)

IEEC owns the copyright of this document which is supplied in confidence and which shall not be used for any purpose other than that of which it is supplied, and shall not in whole or in part be reproduced, copied,or communicated to any person without written permission from the owner.

General features (I) • GOLD-RTR stands for “GPS Open Loop Differential Real Time Receiver”. It’s purpose is to give the same products as the PARIS Aircraft Demonstrator (PAD):

Functionality: computes in Real-Time the PRN code complex correlation functions around the peak (waveforms) for all the selected GPS visible satellites. Applications: The instrument can be used in both altimetry&scatterometry

(PARIS), but also in occultation experiments.

General features (II)• The instrument is divided in two physical devices: a PC laptop running under LINUX and a rack with the custom instrumentation

Laptop: 3 kg weight, 30x30x4 (cm), 30 W power (220 AC, 50 Hz)Rack: 20 kg weight, 35x45x55 (cm), 60 W power (220 AC, 50 Hz)

both parts are linked via an UTP ethernet cable (RJ45 connectors, cat.5)

Instrument parts description (II)

RACKBACK PANEL: Picture overview

RFConnectors

Cooling fanholes

RJ45ethernet connector

Power con.and switch

Instrument parts description (IV)

RACKINSIDE contents: Graphical overview

Instrument parts description (V)

RACKSP: Graphical overview

User’s instrument operation (VI)SOE file preparation software (snapshot)

User’s instrument operation (VII)Instrument control Software

• It is a GUI that makes it easy to the FO actor to control the instrument, either to perform readiness tests or to upload a SOE file to perform an experiment.• When the GUI is started, a window appears (these are 2 examples of the same):

Left: the GUI is not receiving flags information from the RACKRight: The GUI is receiving information from the RACK

User’s instrument operation (IX)Rediness Test Graphical Results