a review of the transponder calibration activities in the frame of the gavdos project h ausleitner,...

A review of the transponder calibration

activities in the frame of the GAVDOS project

HAUSLEITNER, W.(1), J. WEINGRILL(1), F. MOSER (1), J.-D. DESJONQUERES (2),

N. PICOT (2), S.P. MERTIKAS (3)

(1) Austrian Academy of Sciences, Graz, Austria

(2) Centre National d’Etudes Spatiales (CNES), Toulouse, France

(3) Technical University of Crete, Chania, Greece

2IWF/ÖAW GRAZ

The GAVDOS Project

GAVDOS – Establishment of a European radar altimeter calibration and sea-level monitoring site for Jason, Envisat and EURO-GLOSS

Objectives

Establish an absolute sea-level monitoring and altimeter calibration permanent facility on the isle of Gavdos

Conduct tide-gauge measurements as well as direct altimeter transponder, Global Positioning System (GPS), Doppler Orbitography by Radio-positioning Integrated on Satellite (DORIS) and Satellite Laser Ranging (SLR) measurements for altimeter calibration

Deliverables

Jason absolute altimeter bias, Marine geoid, Sea level variations, local deformations / land displacements, etc.

3IWF/ÖAW GRAZ

Gavdos Calibration Work

Calibration of satellite radar altimeters a Gavdos Cal/Val facility using three different methodologies (S.P. Mertikas, et.al. 2010)

Comparing sea level anomalies between the satellite and the in-situ observations

BIAS = SSH_altim – SSH_tide_gauge ≈18±5 cm

Relate measurements to the Mean Sea Level of CLS01_MSS

BIAS = SSH_altim – MSS_CLS01 – SLA_tide_gauge

Usage of a microwave transponder placed at the satellites ground-track

BIAS = ALT_altim – range_altim – H_TRP

4IWF/ÖAW GRAZ

Microwave Altimeter Transponder

The principle of a microwave altimeter transponder is to receive, amplify and retransmit a satellite radar altimeter pulse.

The emitted pulse is received by the altimeter on-board the satellite again with the 2-way travel-time of the pulse giving the range between the satellite and the transponder

Technical specifications

Minimal distortion of the signal

High frequency stability

Frequency: 13.7 GHz

Bandwidth: 600 MHz

High amplification rate

Total gain: 77 dB

Stable instrument delay

Response delay: 13.24 ns

5IWF/ÖAW GRAZ

TRP Location Deployment on Gavdos at DIAS

Cross-over of Jason

3 km apart of Envisat

ITRF2005 coordinates

GPS campaign by S. Mertikas (Nov. 2010)

Φ = 34°49‘17.2953“

λ = 24°05‘27.6631“

h = 251.5627 m

6IWF/ÖAW GRAZ

TRP Site Setup

Housing

Aluminium frame enveloped with fabric

Cover plate from acrylic glass

Protection from wind, dust contamination, animals, etc.

Electrical Power Supply

12 V car batteries

recharched by solar panels (2x50 W)

Modem Telecommanding

Watchdog timer (daily at 0.0h)

GSM/GPRS-modem for remote controlled TRP switch-on

7IWF/ÖAW GRAZ

Ocean vs. Point Target Response

IWF/ÖAW GRAZ

8IWF/ÖAW GRAZ

The Transponder Principle cont‘d

(Envisat Picture)

IWF/ÖAW GRAZ

OSTM Level-2 S-IGDR Data Files

1 Hz / 20 Hz data

Ku / C-band waveforms

Latency: 2 days

Provided by CNES

9IWF/ÖAW GRAZ

ENVISAT Calibration Two years ENVISAT calibration campaign

TRP approx. 3km outside of footprint center

RA-2 set to Preset Loop Output (PLO) mode

RA2/MWR products analyzed RA2_science_level-1b

RA2_average_waveforms

RA-2 instrument bias: 39.0±3.3cm

(Cristea at.al., TGRS-20067-0032)

10IWF/ÖAW GRAZ

Jason Calibration Poseidon-2/3 instrument characteristics

Dual-band (C/Ku) pulse compression radar

128 waveform samples

Frequency / PRF / t-res. = 13.575 GHz / 2060 Hz / 3.125 ns

Operation modes

Acquisition mode: Detects ocean returns and init. Tracking loops

Tracking mode: Nominal mode for the altimeter

Problem: The TRP signature is not visible in the waveform data

Because: ▶ J-Tracking is more sensitive to coast/land transitions generating loss of tracking resulting to a 1.5 sec data gap (desc. passes)

▶ Gavdos is small enough to keep tracking the sea shifting the TRP outside of the altimeter ranging window (asc. passes)

Calibration 2: Measures the transfer function of the internal receiver channel

11IWF/ÖAW GRAZ

Cal-2 Calibration Data

3.125 ns

0.153 s

32 In

divi

dual

Cal

ibra

tions

128 bins20 40 60 80 100 120

5

10

15

20

25

30

Calibration-2 Mode

NO absolute epoch time available!

Dating of individual calibrations is known with 1s accuracy only

Calibration Processing Concept

12IWF/ÖAW GRAZ

13IWF/ÖAW GRAZ

Cal-2 Calibration Configuration

11 sec data gap

5 sec calibrationwaveforms ±1s±1s

14IWF/ÖAW GRAZ

Data Screening

Pass 050 Cycle 018

28oE

coasttransponderoceanland

Measurement Surfacetype

26oE 28oE 30oE

coast

transponderocean

land

KU - Measurements errors

20oE 22oE 24oE 26oE 28oE 30oE 30oN

32oN

34oN

36oN

38oN

40oN CoastTransponderKU measurementHeight < -130mHeight > 100mRange

KU >1450km

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3

Pass 018 Cycle 050

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3

Pass 018 Cycle 050

15IWF/ÖAW GRAZ

Data Interpolation Densification to 20 Hz rate (cubic spline interpolation)

Precise computation of point of closest approach

11s GavdosCrete

(φ,λ)

φ

λ

16IWF/ÖAW GRAZ

Individual Calibration Analysis Definition/Estimation of maximum power reflection by

1)Maximum value of received energy

2)Max. val. of Gaussian fit to return power

3)Half ma. power at leading edge of Gaussian fit

4)Centroid of received energy

0 20 40 60 80 100 1200

100

200

300

400

bins

rece

ived

en

erg

y

Cal-2 ii=8

2)bin # 108.2

3)bin # 102.0

4)bin # 108.4

received energygauss fit2)bin of gauss

max3)bin of leading edge4)centre of received endergy

0 20 40 60 80 100 1200

100

200

300

400

bins

rece

ived

en

erg

y

Cal-2 ii=17

2)bin # 42.3

3)bin # 41.7

4)bin # 42.5

received energy

gauss fit

2)bin of gaussmax

3)bin of leading edge

4)centre of received endergy

Individual Calibration Fitting

17IWF/ÖAW GRAZ

Optimal Parabola Fit

18IWF/ÖAW GRAZ

20 40 60 80 100 120

5

10

15

20

25

30

Cal-22)bin of gauss

max3)bin of leading edge4)centre of received endergy

32 In

divi

dual

Cal

ibra

tions

128 bins

19IWF/ÖAW GRAZ

Power Vertex Adjustment Alignment of PCA of orbit vertex of fitted parabola

• Absolute time of PCA from orbit

• Absolute dating of bin #1 of individ. cal. #1

Altimeter range command

Set for each calibration

Provided by CNES on a pass-per-pass basis

Ranging ambiguity

20IWF/ÖAW GRAZ

Geophysical Parameters

Source Uncorr. effect

Cycle 50Corr.

Wet

Troposph

0-30 cm 15 cm

Dry troposphere

230 cm 229.5 cm

Iono troposphere

0.2-20 cm

1.6 cm

Sea state bias

0-20 cm 8.8 cm

Range

WetTroposph.

DryTroposph.

Ionosph.

Sea State Bias

DOY

Range Correction

21IWF/ÖAW GRAZ

-2.49 m

[m]

DOY

[m]

Sea Surface Height

22IWF/ÖAW GRAZ

Geophysical Correcitons

23IWF/ÖAW GRAZ

Cal-2 Ranging Budget / Residual

24IWF/ÖAW GRAZ

r

Geoid

Ellipsoid

Calibration bin rangeAmbiguityAltimeter delayCoM CorrectionDry troposphereWet (water vapour)Ionosphere

TRP delay (electronic)TRP delay (geometric)Station marker eccentricitySlant range correction

TRP ell.heightSolid earth tides

Corrections

Effect Magnitude (m)

Orbital heightResidual

33738.0881310718.858 -5.173 0.471

- 3.972 -1.477 -0.824

251.169 -0.060

1344398.967 44.575

-2.297-0.116-0.016

25IWF/ÖAW GRAZ

Outlook Analysis of full set of Cal-2 passes

Limitednumber ofpassesavailable

Usage of precise orbits

Provided with a 60 days latency

DIODE DEM coupling mode

Usage of onboard digital elevation model for pre-definingthe altimeter tracking window

Transponder calibration withnominal tracking rate (51 ms)

Pass Cal Status Data

Date Cycle OK / fail S-IGDR SIMPACAL Cal. range Aux. Data

09 09 12 44 OK YES YES

09 09 22 45 fail YES YES


09 10 11 47 OK YES YES

09 10 21 48 no CAL

09 10 31 49 OK YES

09 11 10 50 OK YES YES YES

09 11 20 51 fail YES

09 11 30 52 no CAL YES

09 12 10 53 no CAL YES

09 12 20 54 no CAL YES

09 12 30 55 no CAL YES YES



Pass Cal Status Data

Date Cycle OK / fail S-IGDR SIMPACAL Calibration Aux. Data










10 04 28 67 no CAL YES

10 05 08 68 OK YES YES

10 05 17 69 fail YES

10 05 27 70 OK YES YES

10 06 06 71 OK YES

10 06 16 72 fail YES

Figure Pool

26IWF/ÖAW GRAZ

Geophysical Corrections

27IWF/ÖAW GRAZ

Mean sea surface

Solid Earth tide

Geocentr. Ocean tide

Pole tide height

Inv. barom. height eff.

HF fluctuations of SST

28IWF/ÖAW GRAZ

Sea Surface

Ellipsoid

Slant Distance

TRP

Range_ku

Orbit

SSH

Altitude

Date 2009/11/10

Time 14:19:34

Date Exec. CAL2

Only known to integerseconds ?

Ho 4604232

LSB Ho .0073191 m

NSPEC 3

NCAL 32

a review of the transponder calibration activities in the frame of the gavdos project h ausleitner,...

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