AERODYNE RESEARCH PROPRIETARY

SPEAR-TIP

Technical ReviewJuly 19, 2001

Aerodyne Research

45 Manning Road

Billerica, MA 01821-3976

(978) 663-9500

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Aerodyne Agenda

• POLMODTRAN Validation Plan– Overview

– Basic Plan

– Long Term Plan

• SPEAR Status– Task 1: VIS-SPEAR Sensor Build

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POLMODTRAN Validation

• Determine what data exist (9/1).

• Identify most significant variables (9/1).

• Identify additional data collection necessary (9/1).

• Long term plan (10/1).

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Overview of Proposed Plan

• Verify Requirements: validation scenarios

• Significant issues:– Impact of aerosols on polarimetry

– Available polarimeters

– Existing data

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New Data Collections (minimal)

• Make (VMP) polarimetry measurements at Aeronet site(s).– Aeronet has established aerosol measurement

suite.

– Numerous sites around the world.

• Measurement geometry:– Meridianal (in solar plane).

– Almercanter scan at zenith angle approx. 60 degrees.

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New Collections (“2nd Phase”)

• Introduce VIS-SPEAR after sufficient preliminary sensor validation.– Continuous and broader spectral coverage.

– Faster data collect.

• Co-collect with VMP.• If necessary to decompose scattering by

individual species, introduce Aerosol Mass Spectrometer (ARI).

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Summary of Existing Polarimetry Data

• Research Scanning Polarimeter (RSP)

– NASA Goddard Institute for Space Studies Data Collection Contract with SpecTIR

– Nine Channel VNIR Polarimeter, Prototype for Earth Observing Scanning Polarimeter

– Approx 25 Flights

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Significant Variables

• Case for aerosol retrieval goes here.

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Task 3: Field Testing

• Field test objectives to include MODEL VALIDATION and SENSOR VALIDATION.

• Consider including AEROSOL MEASUREMENTS to the test plan.

• Design test(s) and SELECT SITE(S) to accomplish these objectives most effectively.– Hanscom AFB Rooftop

– Wright-Patterson AFB Tower

– Aeronet Sites

– Millstone Hill (MIT Lincoln Lab)

– Kirtland AFB Tower

– Huntsville Tower

– Elsewhere...

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Aerodyne AMS

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SPEAR-TIP Project Plan

• VIS-SPEAR Sensor - Longest lead times

– APS Optomechanical Design & Fab. (Design in process, 3-4 wks. to complete, 8-9 wks. fabrication if glass available)

– Andor Tech. CCD Imager (Ordered 7/6, 6 wks.)

– Pol. Mod. Components (2-4 wks., not yet ordered)

– Labsphere Cal. Source (Ordered 7/17, 2-3 wks.)

– Integration at ARI (HW, SW, Cal., 8 wks. after delivery of CCD)

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PSIM Sensor Layout (SOW)

CollectionOptic(focusable)

CCDVideoCamera

ManualReflexMirror

PolarizationModule(focusable)

Convex GratingSpectrometerApprox. 15x13x10cm

DetectorInterface(hard mount)

CCD Imager

Slit

APS Bids Bold BoxesARI Supplies Others

MechanicalShutter

FieldStop

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Optical Performance

• Diffraction limited up to spectrometer slit (specification).

• 15 degree total FOV. Could be relaxed if impossible to achieve performance otherwise.

• Wavelength range: 400-2200 nm for lens design. Single octave subbands for particular sensor configuration.

• Primary lens design: 4 elements including 2 doublets. Three identical lenses required for sensor.

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Collection Optic

• Focal Length Approx. 50 mm.• Max f/2, manual iris.• FOV 15 degrees.• Entrance window < 38 mm to accomodate

calibration source.• Custom refractive design.

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VIS-SPEAR Objective Lens

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VIS-SPEAR Objective Lens

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VIS-SPEAR Objective Lens

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Self Polarization Effects

• Contributors to self polarization:– Intrinsic birefringence of glass

– Stress birefringence of lens grinding/polishing process

– Stress birefringence of mount

• Measures to avoid self polarization:– Use glass w/ low birefringence (high quality grade):

retardance = 4 nm/cm.

– Design mount and assemble to avoid excessive stress on optics.

– As part of alignment, rotate lens groups for minimum birefringence. Only first two lens groups will contribute to measurement error.

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Reflex Mirror

• Necessary for aiming sensor in the field.• Beamsplitter is undesirable due to signal loss.• Manually actuated reflex mirror.• Optical performance is not necessarily critical

but the latest design is quite good (6 element, well corrected).

• Manual focuser for small CCD w/ c-mount

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VIS-SPEAR Relay (1/2)

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VIS-SPEAR Relay (1/2)

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Mechanical Shutter

• CCD imager does not have integral shutter.• No room between spectrometer and imager

(0.235”).• Placement is not extremely critical. In front of

polarization module is a likely location.

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Polarization Module

• Two quartz waveplates and an analyzer in a well collimated beam.

• Custom waveplate thicknesses TBD. Approx. 1-10 mm thick.

• Bandpass filter to limit wavelength range to a single octave to avoid overlapping orders in spectrometer.

• Ability to adjust for focus on spectrometer slit.

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Polarization Module (cont.)

• ARI will want ONLY ONE polarization module but it must be possible to interchange waveplates.

• Dichroic sheet analyzer to achieve high purity and high throughput -- as compared to prisms.

• Optic axes of waveplates must be oriented 45 deg. w/ respect to each other.

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Polarization Module Optics

Quartz WaveplatesArrows indicate optic axis

DichroicPolarizer

Direction of Propagation

Baseplate Orientation

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Convex Grating Spectrometer

• Agilent VS-15 – http://www.agilent.com/cm/diffract/VS15.shtml

• Offner relay, holographic grating, 100 nm/mm dispersion, f/2. Consider having larger dispersion grating fabricated (probably holographic).

• Current slit width 12 um: undersampled w/ 24 um pixels. Consider having larger slit(s) fabricated.

• Aerodyne will furnish to APS for mechanical integration.

• Slit is 0.710” behind mounting flange.• Back working distance is 0.629”.

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Detector Interface

• Mechanical interface between spectrometer and CCD imager.

• No focus necessary -- hard mount.• No X-Y translation necessary.• No rotation adjustment.• ARI will provide flange-to-flange distance for

focus. APS designs and fabricates spacer (i.e. interface).

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Andor DV412 CCD Imager

• TE Cooled (-60C in air), thinned, back illuminated detector array.

• Large pixels - 24x24 um. Total chip size 12.3 x12.3 mm (512 x 512).

• 1 Mpixel/s readout, 10e- ro noise typical.