AltiKa Radiometer performance assessment

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AltiKa Radiometer performance

assessment

R. Rodriguez Suquet &

N. Steunou, J.L. Courrière

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Overview

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Radiometer Instrument Definition

■

Radiometer Architecture

Radiometer Calibration

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Radiometer Performance Test Results

Performance Tests at Instrument Level

•

Compatibility Test

Assembly, Integration and Test (AIT)

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Overview

■

Radiometer Architecture

■

Radiometer Performance

•

Compatibility Test

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Radiometer Parameters Design (1/2)

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Basically, the AltiKa Radiometer is required to correct the

contribution of wet troposphere path delay to overall altimeter

range measurements.

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Dual frequency channel microwave Radiometer:

23.8 GHz+/- 200 MHz: Brightness temperature measurements give

information related to the

water vapor content

.

37 GHz +/- 500 MHz: Brightness temperature measurements give

information about

cloud liquid water

.

Both measurements are required to correct the wet troposphere on

altimeter measurements.

■

Both Brightness Temperatures in addition to the altimeter

estimated Backscatter coefficient

σ

₀

are applied to calculate the

troposphere correction range.

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Radiometer Parameters Design (2/2)

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Blanking Signal for

altimeter emission

protection

■

Calibration

measurements:

one cold and one hot

■

Direct Power Detection

Radiometer Parameters Parameter _Value Radiometer band 23.8 GHz + 200 MHz 37 GHz + 500 MHz Pointing Nadir Polarisation Linear Radiometric resolution (requirements) K-band : < 0.4 K Ka-band : < 0.3 K Radiometric accuracy < 3 K Radiometer averaging 200 ms Antenna Parameters Parameter Value

Antenna apertures K-band : 0.85°

Ka- band : 0.6°

Cold Feed efficiencies K-band : freq>99%

Ka-band : freq>99%

Nadir Antenna efficiencies K-band : freq>94%

Ka-band : freq>96% Radiometer Working

TXpulse RXecho TXpulse RXecho

Radiometer Working

Pulse Duration

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Overview

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•

Compatibility Test

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Switch between 2 calibration types

Hot:measures the thermal emission of an internal load

Cold:sky antenna to get the cold reference point

-Interfaces (TM/TC) with the platform -Chirp pulse generation

-Echos reception and processing from the altimeter (tracking and acquisition)

-Digital processing of the radiometer signals

- Temperature amplification

-RF detection (‘direct power detection’) and filtering -Transmission of the generated video voltages to BT

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5 measurements cycles are produced within 1s.

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Radiometer calibration based on:

2 Calibration Feeds: Sky Horn and Internal Load

Measurements Cycle Time: 200 ms

(depending on the current PRF value and the altimeter mode)

Time between calibrations: 3 seconds

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Overview

■

Compatibility Test

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Radiometer Performance Tests at Instrument Level

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Calibration of the radiometric model developed by TAS-F

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Estimation of the radiometer performances in terms of:

sensitivity

absolute accuracy

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Radiometric target in front of antenna horns are used for

tests in thermal vacuum

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Brightness Temperature Dynamic :

8 measurement points going from 110 K until 300 K

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Radiometric Absolute Accuracy (1/2)

Antenna Temperature Absolute Accuracy in K band

-1,00 -0,80 -0,60 -0,40 -0,20 0,00 0,20 0,40 0,60 0,80 1,00 110 135 160 185 210 235 260 285 310 Ta (K) A bs ol ut e A ccu ra cy ( K) 40°C TV St ep (n°1) 0°C TV St ep (n°2) 20°C TV St ep (n°3)

Total Absolute Accuracy (with reflector characteristics)

< 0.4 K

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Radiometric Absolute Accuracy (2/2)

A nt e nna Te m pe r a t ur e A bsol ut e P r e c i si on e n ba nde K a

-1,00 -0,80 -0,60 -0,40 -0,20 0,00 0,20 0,40 0,60 0,80 1,00 100 125 150 175 200 225 250 275 300 325 T a ( K ) Palier 40°C (n°1) TV Palier 0°C(n°2) TV Palier 20°C(n°3)

Antenna Temperature Absolute Accuracy in Ka band

-1,00 -0,80 -0,60 -0,40 -0,20 0,00 0,20 0,40 0,60 0,80 1,00 110 135 160 185 210 235 260 285 310 Ta (K) 40°C TV Step (n°1) 0°C TV Step (n°2) 20°C TV Step (n°3)

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Radiometer Resolution (1/2)

Antenna Temperature Sensitivity in K band

0 0,05 0,1 0,15 0,2 0,25 0,3 110 135 160 185 210 235 260 285 310 Ta (K) S en sit iv it y (K ) 40°C TV Step (n°1) 0°C TV Step (n°2) 20°C TV Step (n°3)

Input Nadir Antenna Sensitivity < 0.15 K

Total Sensitivity (with reflector characteristics)

< 0.17 K

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Radiometer Resolution (2/2)

Antenna Temperature Sensitivity in Ka band

0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 110 135 160 185 210 235 260 285 310 Ta (K) Se ns it iv it y( K) 40°C TV Step (n°1) 0°C TV Step (n°2) 20°C TV Step (n°3)

Input Nadir Antenna Sensitivity < 0.17 K

< 0.19 K

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Radiometer/Altimeter Compatibility Tests

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Dedicated tests have been performed in order to check the

compatibility between altimeter and radiometer in the following

context:

For all altimeter operational modes

Without and with antenna connected

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Neither an impact on radiometric bias or on radiometric

sensitivity has been recorded

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Radiometric Absolute Accuracy (1/2)

Input Nadir Antenna Absolute Accuracy

< 0.4 K

< 0.8 K

Required Absolute Accuracy < 3 K

Antena Temperature Absolute Accuracy in K band

-0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 AIT Test Absol u te Acc u racy ( °K ) TV Pre-TV Postvib Initial Payload Initial Instrument Previb

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Radiometric Absolute Accuracy (2/2)

Input Nadir Antenna Absolute Accuracy

< 0.8 K

< 1 K

Antena Temperature Absolute Accuracy in Ka band

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 AIT Test A b so lu te A c cu racy ( °K) TV Pre-TV Postvib Initial Payload Initial Instrument Previb

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Radiometer Resolution (1/2)

Input Nadir Antenna Sensitivity < 0.16 K

< 0.17 K

Required Sensitivity < 0.30 K

Antena Temperature Sensitivity in K band

0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 AIT Test S e n s iti v ity (° K ) TV Pre-TV Postvib Pre-vib Initial Payload Initial Instrument

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Radiometer Resolution (2/2)

Input Nadir Antenna Sensitivity < 0.17 K

< 0.19 K

Required Sensitivity < 0.40 K

Antena Temperature Sensitivity in Ka band

0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.2 AIT Test S e n s itiv ity ( °K ) TV Pre-TV Postvib Initial Payload Initial Instrument Previb

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Summary of Performance Results

Characteristics &

Performances

Ka - Band

K- Band

Results

Spec

Results

Spec

Sensitivity

(including reflector

contribution)

< 0.19 K < 0.4 K

< 0.17 K

< 0.3 K

Absolute Accuracy

(including reflector

contribution)

< 1.3 K

< 3 K

< 1.0 K

< 3 K

Nadir Antenna Efficiency

99.6 %

> 99 %

99.5 %

> 99 %

Cold Feed Efficiency

97 %

> 96%

94.6 %

> 94 %

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Overview

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Radiometer Performance

Compatibility Test

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CONCLUSION & OUTLOOK

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During instrument performances tests all radiometer instrument

performances have been reached.

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These results prove a very good instrument stability on the

overall tests.

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After instrument calibration, the updated radiometric model

have been implemented in ground processing segment to

retrieve the Brightness Temperature.

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The AIT test results contribute successfully to the validation of

the Payload Instrument Module (PIM).

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Further AIT tests are being performed to achieve a complete

validation.

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Questions or Remarks ?

Thanks for your attention

Contact :

[email protected]

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Blanking Signal Protection

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Radiometer is in operation during the altimeter reception echos in

order to avoid any possible perturbations on radiometer measurements

coming from the altimeter emission.

Radiometer Working

T_Xpulse R_Xecho T_X pulse R_Xecho

Radiometer Working

Pulse Duration

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Radiometer Architecture (2/2)

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Radiometer BHR is based on a ‘Direct Power Detection’ architecture

for each frequency channel.

T_A

Pre-Detection G’ Gain-B Band-Noise Trec’

Integrator (low-pass filter) C A N Calibration Feeds Post Integration T_A’ BHR V_x Detection