Doppler Wind and Temperature Sounder: A breakthrough technique GATS Proprietary Larry Gordley, GATS...

Doppler Wind and Temperature Sounder:A breakthrough technique

GATS Proprietary

Larry Gordley, GATS Inc.

Dave Fritts, GATS Inc.

Tom Marshall, GATS Inc.

COSPAR Scientific Assembly 2012Mysore, India

DWTS Instrument OverviewSpecifications:• Mass – 8 kg• Power – 12 W• Volume ~36x23x22 cm • Data rate < 30 kbps with low alt wind • Three 5.0 cm aperture thermal IR cameras

NO (hi alt) 1829 – 1873 wn13CO2 (mid alt) 2258 – 2282 wn,

N2O (for low alt wind) 2120 – 2160 wn• Static limb viewing, 20° FOV at velocity normal • T, V, N2O and 13CO2 mixing ratios, VER (NO and CO2)

Single telescope two-channel design above, hasevolved to three independent cameras, below.

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Temperature

Measures Low Pressure Doppler Broadened Emission

Line Width is proportional to square root of kinetic

temperature

ν (wavenumber, frequency)

Single Atmospheric Emission line

1

Emission lines are typically a few thousandths of a wavenumber wide, requiring optical resolving powers of 100,000 or more to measure.

Typically, good spectrometers achieve 10,000. DWTS achieves >300,000.

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Doppler Shift Measurements

Broadband emission will not detect Doppler shift, nor will

spectra measurements, unless there is a zero shift reference

Doppler Spectral shift due to line-of-sight (LOS) relative air velocity

shift, Δν


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Atmospheric spectral emission from one line 0

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Atmospheric spectral emission from one line

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A Gas Filter Reference

DWTS “Notch” filter Approach

By viewing through a sample of the emitting gas, a filter is

produced that causes a drop in signal during the Doppler

Integration Pass (DIP) through the zero shift position

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Add Gas Cell – One Emission Line Example.Gas cell acts as high resolution notch filter and

effectively serves as the zero shift reference point.

The “shift, Δν ” is the spectral separation of the cell spectra (black absorption feature) from the observed

atmospheric spectra (red emission feature).

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Cell Absorption and Atmospheric Emission

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Add Gas Cell – One Emission Line Example

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DIP width is proportional to square root of cell temperature

+ atmospheric temperature

shift, Δν


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Multi-line Effect

The emission lines that match the corresponding cell gas lines (i.e. “notch” filters), are scanned simultaneously, producing a DIP signal consistent with the total multi-line emission. The DIP

width is the same as the single line DIP.

Two Line Example

Cell Absorption & Atmospheric Emission, two lines

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Two Line Example

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Two Line Example

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Two Line Example

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Two Line Example

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Two Line Example

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Orbit Implementation

By imaging the limb, normal to the spacecraft (SC) velocity vector, air parcels at all altitudes will produce a DIP signal as they traverse the FOV (i.e the 2D detector array).

The animation tracks just one exaggerated Limb Air Volume

(LAV).


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y

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Altitude

Δν (wavenumber) shift

DWTS FOVImaged on 2D Detector FPA

z

-10° +10°0° Angle from Velocity Normal

Relative Air Velocity due to SC

SCVelocity

Limb Air Volume (LAV)viewed from above

Limb Air Volume (LAV)

Implementation, In-Orbit Observations

Observations Through Limb Atmospheric Volume

Above, Spectra and Signal from one LAV

Figures below depict observation geometry

Observation Vectors

shift, Δν


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LAV

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In-Orbit Observations

Angle from Velocity Normal


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shift, Δν


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SCVelocity



140 different observation

angles during pass through FOV

140 shift observations as LAV passes through FOV


Angle from Velocity Normal(140 observations across FOV)


Observation Vectors



shift, Δν


0Observation Angle

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LOS Wind

Finite Line-of-Sight (LOS) wind will change the zero shift position.

The zero shift position for zero

wind is known to ± <0.1 m/s due to knowledge of SC velocity (± <<1m/s) and attitude (± <3

arcsec). Also, precise attitude knowledge permits statistical

calibration in orbit.

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SCVelocity



with ≅250 m/s LOS wind

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Apparent zero relative air

speed (shift) with ≅250

m/s LOS wind



Observation Vectors

In-Orbit Observations – LOS Wind Effect



shift, Δν


0Observation Angle

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The “Shift/Angle” Scale

Spectrally close lines (such as Lambda doublets for nitric oxide)

provide the measure of “shift/angle” scale.

The observed angle separating doublet DIP features is proportional

to relative AT air speed, which is proportional to SC velocity plus AT

wind.

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Doublet Example

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Observation Vectors



In-Orbit Observations - Doublet Effect

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Doublet Example


Doublet Effect



Observation Vectors



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Doublet Example


Doublet Effect



Observation Vectors



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Doublet Example


Doublet Effect



Observation Vectors



shift, Δν


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Doublet Example


Doublet Effect



Observation Vectors



shift, Δν


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Velocity

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Doublet Example


Doublet Effect



Observation Vectors



shift, Δν


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Doublet Example


Doublet Effect



Observation Vectors



shift, Δν


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Doublet Example


Doublet Effect



Observation Vectors



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Doublet Example


Doublet Effect



Observation Vectors



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Doublet Example


Doublet Effect


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AT Wind Measurement

The AT wind stretches or contracts the “shift/angle”

scale, providing the AT wind estimate.

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Doublet Example

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shift, Δν

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Velocity

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In-Orbit Observations - Along Track (AT) Wind Effect

AT = 0 m/s



AT ≅ 700 m/s(AT same direction as SC)



Observation Vectors



0Observation Angle

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Current

Measurement Systems

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Current Measurement Systems

T, W2T, W1W1None

D

15 km2540

100

150

200

250 km N

T = Temperature, W1 – One Vector Wind, W2 – Two Vector Wind

Day Night

1 2 3 4 5 6

Typically a narrow slit, observing at a 45° degree angle to the spacecraft velocity vector, creates a spectrum that is used to deduce LOS Wind. The slit observations

are averaged from 150 km to sometimes over 700 km to obtain required S/N, producing an average wind over those same along-track distances.

Altitude range of current technology

products

150 km to700 km

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DWTS

Measurement Systems

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DWTS Measurement SystemAs the atmospheric limb air passes through the DWTS FOV, it is observed with 10 km resolution and at 140 different Doppler shifts. This provides the information necessary to infer profiles of wind and temperature (depicted by colored air emerging from the FOV) at a 7 km along-track

spacing with a 10 km along-track resolution. The FOV acts as an assembly line that produces a wind and temperature product for narrow air volumes.

T = Temperature, W1 – One Vector Wind, W2 – Two Vector Wind

Altitude range of DWTS products T, W2

T, W1W1None

D N

15 km2540

100

150

200

250 km

-10° +10°

DWTS FOV1000 km

0°

Day Night

Processed Profiles are Spaced at 7 km with 10km along-track resolution

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Summary

DWTS uses Gas Filter Correlation Radiometry and a simple, moderately cooled, static MIR camera to measure Wind and Temperature

from cloud-top to over 200 km day and night.

Considering cost, global coverage, continuity, spatial resolution, diurnal

capability, altitude range and simultaneity of Wind and Temperature, DWTS is projected to advance our capability of remotely sensing

upper atmosphere wind and temperature by more than 3 orders of magnitude.

GATS Inc.11864 Canon Blvd., Suite 101Newport News, VA 23606 USAwww.gats-inc.com

GATS Proprietary

Larry Gordley [email protected]

Dave Fritts [email protected]

Tom Marshall [email protected]

Doppler wind and temperature sounder: new approach using gas filter radiometry

Larry L. Gordley and Benjamin T. Marshall, “Doppler wind and temperature sounder: new approach using gas filter radiometry”, J. Appl. Remote Sens. 5, 053570 (2011)

Doppler Wind and Temperature Sounder: A breakthrough technique GATS Proprietary Larry Gordley, GATS...

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Transcript of Doppler Wind and Temperature Sounder: A breakthrough technique GATS Proprietary Larry Gordley, GATS...