IRDC Theory and practice of building instruments for diffuse reflectance measurements

IDRC-2016

The theory and practice of building

instruments for DR measurements

Jerome Workman

Unity Scientific and National University

IDRC-2016

Outline

• Light Interaction with Matter

• Sampling Accessories

• Illumination/Measurement Geometries

• The Integrating Sphere and Integrating Sphere Type Measurements

• Reflectance Theory: Review

• Instrument Parameters Affecting Spectra

• Problem Highlighted: Distance to Detector

Light Interaction with Matter

Light interaction with solid materials. Ray tracing indicates the possible outcomes for

individual photons from the incoming beam.

Specular Reflection

Diffuse Reflection

Absorption

Transmittance

Interaction

Scattering

Rayleigh Scattering

Color/Electronic Absorption

Am

plit

ud

e

Wavelength (nm)

Effective Pathlength

Absorptivity

200 1150 2500

Light Interaction in Transmittance

Sample Attenuates the

Light

Sample Layer

I0 I

hν

100% Initial Light

% Attenuated or Absorbed

Light

I0 Sample Beam Sample Detector Optics

Detector

I

None

Cuvet

Large Lens

Small Lens

Beam Geometries of Various Transmission Measurements

Light Interaction with Particles in Diffuse Transmittance

Sample Attenuates the

Light

Sample Layer

I0 I

hν

Particles cause Scattering

Losses

Particles cause Scattering

Losses

100% Initial Light

% Attenuated or Absorbed

Light

Light as Specular Reflection (Elastic Collision)

Reflective Surface

Specular Viewing Angle

I0 Elastic

Collision with no light

Interaction with Sample

Normal Angle (0°)

~I θ θ

Light as Diffuse Reflection (Inelastic Collision)

Diffuse Surface

Sample Layer

I0 Inelastic

Collision with light

Interaction with Sample

Normal Incidence Angle (o°)

I Θ = 45°

Angular Distribution of Reflected Light

Diffuse Surface Sample Layer

Lambertian Reflection

B S0 cos α

B cos ϑ

α

ϑ

From G. Kortum, Reflectance Spectroscopy

Illustration of Terms for Angular Distribution of Reflected Light

Sample Layer


α

ϑ dϑ

dω

df

I0 I


Angular Reflected Energy Distribution


Lambertian Angular

Distribution

B S0 cos α

B cos ϑ

α

ϑ

Seeliger Angular

Distribution


Sampling Accessories

Locking powder cup – optical view

Top View

Powder Cup

I0 I

Side View

Reflective Back

Window

Fine ground sample

Sample

Transflectance

I0

Diffuse Reflective Back

Sample

Optical Window

I I0 I

Physical Pathlength

Optical Pathlength

Liquid transflectance cell

Liquid Transflectance Cell

Top View

I0

I

Side View

Physical Pathlength is physical distance where photon passes through, e.g. 0.3 mm nominal

Effective Pathlength is optical distance where photon passes

through: ~ 0.3 mm x 2.5 = 0.75 mm

Diffuse Reflective back

Optical Window

Liquid Sample

Locking powder cup – optical view

Top View

Powder Cup

I0 I

Side View

Liquid cuvet and powder cell types

Top View

Powder Cup

I0 I

Side View

Powder Cup (Top and Bottom Sections)

External Reflectance Regimes

Specular surface

θ1 θ2

Θ1 = Θ2

Specular external reflectance

I0 I

θ1 θ2 Reflection/absorption or Transflectance

I

Θ1 ‡ Θ2

I0

Reflective Surface

Sample absorptive surface

Elastic photon collision

Inelastic photon collision

Illumination/Measurement Geometries

0°/45° Measurement Geometry

Detector

I0 I

Θ = 45°

Horizontal Surface

Incident Energy at

Normal Angle

(0°)

Sample

45°/0° Measurement Geometry

Detector

I0 I

Θ2 = 45°

Horizontal Surface

Incident Energy at

(45°)

Sample

Θ1 = 45°

Θ3 = 45° Measure at

(0°)

d/8° Color Measurement Geometry

Detector

I0

I

Θ2 = 82°

Horizontal Surface

Normal Angle to Sample

(0°)

Sample

Θ1 = 8°

22.5°/22.5° Specular/Color Measurement Geometry

Detector

I0 I

Θ2 = 45°

Horizontal Surface

Incident Energy at

(22.5°)

Sample

Θ1 = 22.5°

Measure at

(0°)

Θ3 = 22.5°

Basic Configurations for Variable Measurement Geometry

I0

I

Horizontal Surface Sample

DIFFUSE REFLECTION

I SPECULAR

TRANSMISSION I DIFFUSE

TRANSMISSION

Incident Energy at Normal Angle (0°)

I SPECULAR

REFLECTION

Θ = 5°

Θ = 5°

Θ = 45°

Θ = 135°

Diffuse Reflection Color Measurement Geometry

I0

I

Θ = 45°


DIFFUSE REFLECTION


Diffuse Transmission Color Measurement Geometry

I0


I DIFFUSE

TRANSMISSION


Θ = 135°

Specular Reflection Color Measurement Geometry

I0



I SPECULAR

REFLECTION

Θ = 5°

Specular Transmission Color Measurement Geometry

I0


I SPECULAR

TRANSMISSION


Θ = 5°

Transmitted, Remitted, and Absorbed Energy: Small Area Detection

I

I0

Sample

MEASURED TRANSMITTED


I MEASURED REMITTED

UNMEASURED ABSORBED

Unmeasured Remittance

Unmeasured Transmittance

Unmeasured Transmittance

Remitted, and Absorbed Energy: Hemispherical Detection

I0

Detector I

Light Shield Cylinder

Sample in Reflection

Port

Remitted Reflection

Energy

ABSORBED ENERGY IS NOT

MEASURED DIRECTLY

Transmitted and Absorbed Energy: Hemispherical Detection

I0

Detector I


Sample in Transmission

Port

Transmitted Energy

ABSORBED ENERGY IS NOT

MEASURED DIRECTLY

Light Reflector in Sample Port

Integrating Sphere: Late 1970s Type

I0

Sphere Detector Port

I


Sphere Entrance Port

Two Position Mirror

(Sample and Reference)

Monochromatic Light

Sphere Sample Port

0°/45° Measurement Geometry: Type I

Sample

Window

Detectors

Light Energy – Post-dispersive

0°/45° Measurement Geometry: Type II

Sample Window

Detectors

Light Energy – Post-dispersive Front surface Diagonal mirror

Pre-Dispersive, Grating Single Monochromator Design

Exit Slit

Diffraction Grating

Normal Angle Entrance Slit

Sample

Collimating Optics

Collimating Optics

Shutter

Source

Detector 1

Detector 2

0°/ 45° Reflectance

Exit Slit

Diffraction Grating

Normal Angle Entrance Slit

Detector

Sample

Collimating Optics

Collimating Optics

Shutter

Source(s)

Analog Amplifier and A to D Converter

Controller Board

Computer Board

Power Supply

Electronics

//

//

Post-Dispersive, Grating Single Monochromator Design

45°/0° Illumination

Grating and DLP DMD with Single Element Detector Design Pre-Dispersive Optics

Fixed Diffraction Grating

Normal Angle

Detector

Collimating Optics

DLP DMD

Entrance Slit

Collimating Optics

Shutter

Source(s)


Digital light processing (DLP)—Digital micromirror device (DMD) spectrometer

Grating and Fixed Array Detector Design Pre-Dispersive Optics

Fixed Diffraction Grating

Normal Angle

Fixed Array Detector

Analog Amplifier and A to D Converter

Controller Board

Computer Board

Power Supply

Electronics

//

//

Entrance Slit

Collimating Optics

Shutter

Source(s)


Optical Schematic

Moving mirror

Scanning Michelson Interferometer

Light Source

IR-Source

Light Pipe

Integrating Chamber

J-Stop

Beam Splitter

Fixed mirror

Fixed Mirror

Detector Optics

Michelson Interferometer Design (FT-NIR) - Optics

Detectors

Sample

0°/ 45° Reflectance

The Integrating Sphere

Beam Geometry for Diffuse Transmittance/Transmission Measurements

I0

Sample Beam

Detector I

Optical Sample


Photometric Port or

Window

Inner Reflective Surface of Integrating

Sphere Diffuse

Transmission Energy

I0

Detector I

Optical Sample


Sample Port or Window

Inner Reflective Surface of Integrating

Sphere

Diffuse Reflection

Energy

Beam Geometry for Diffuse Reflectance/Reflection Measurements

Figure showing the distance from the exit port entrance plane to the detector window (δ).

Detector

Detector Port

Integrating Sphere Wall

δ

Integrating Sphere Type

Measurements

Integrating Sphere – Single Beam Reflectance: 0%

I0

Detector I


No Sample in Sample Port

Entrance Port

Integrating Sphere – Double Beam Reflectance: 0%

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I REFERENCE SAMPLE

PORT (100% REFLECTOR)

TEST PORT (NO SAMPLE

PRESENT)

Entrance Port

Integrating Sphere – Single Beam Reflectance: 100%

I0

Detector I


100% Reflectance Material in Sample

Port

Entrance Port

Integrating Sphere – Double Beam Reflectance: 100%

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I REFERENCE SAMPLE


TEST PORT (100% REFLECTOR)

Entrance Port

Integrating Sphere – Single Beam Reflectance: Test Sample

I0

Detector I


Test Sample Material in Sample Port

Entrance Port

Integrating Sphere – Double Beam Reflectance: Test Sample

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I

REFERENCE SAMPLE PORT (STANDARD

REFERENCE MATERIAL)

TEST PORT (TEST SAMPLE

MATERIAL)

Entrance Port

Integrating Sphere – Single Beam Transmittance: 0%

I0

Detector I


100% Reflector in Sample Port

Transmittance Port Blocked

Integrating Sphere – Double Beam Transmittance: 0%

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I REFERENCE SAMPLE


Transmittance Port Blocked 100%

Reflector in Sample Port

Integrating Sphere – Single Beam Transmittance: 100%

I0

Detector I


100% Reflectance Material in Sample

Port

Transmittance Port

Integrating Sphere – Double Beam Transmittance: 100%

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I REFERENCE SAMPLE



Transmittance Port

Integrating Sphere – Single Beam Transmittance: Test Sample

I0

Detector I


100 % Reflector Material in Sample

Port

Transmittance Port with Test

Sample

Integrating Sphere – Double Beam Transmittance: Test Sample

I0

Detector

I

TEST SAMPLE BEAM I0

REFERENCE BEAM

I REFERENCE SAMPLE



Transmittance Port with Test

Sample

Angular Reflected Energy Distribution


Lambertian Angular

Distribution

B S0 cos α

B cos ϑ

α

ϑ

Seeliger Angular

Distribution

Sample Layer


α

ϑ dϑ

dω

df

I0 I


Instrument Parameters Affecting DR Spectra

1. Wavelength accuracy

2. Wavelength repeatability

3. Wavelength linearity

4. Wavelength reproducibility

5. Photometric accuracy

6. Photometric repeatability

7. Photometric reproducibility

8. Photometric linearity

9. Photometric noise

10.Photometric drift

11.Signal averaging integrity (systematic noise component)

12.Instrument line shape

13.Detector response

14.Source color temperature

15.Instrument temperature (thermistor)

16.Sample temperature (thermistor)

17. Technology difference artifacts (FT-DA-M-LVF-DLP-Other)

Readily Measurable Instrument Parameters Affecting Spectra

Detector Response using Dual Channel Ultra-cooled InGaAs

1E+09

1E+10

1E+11

1E+12

900 1100 1300 1500 1700 1900 2100 2300 2500 2700 2900

D*

in c

m H

z1/2

/W

Wavelength (nm)

D* Spectral Response

InGaAs (-30C)

InGaAs (-50C)

PbS (-10C)

PbS(-20C)

Specific Detectivity (D*)

Detector Response time Dual Channel Ultra-cooled InGaAs

0

200

400

600

800

1000

1200

-30C 27C

Detector response Times (μs)

InGaAs PbS

0.01 0.1

-30 °C 27 °C

Measurement issues affecting reflectance spectra

1. Reflectance and transmittance of window from sample cup 2. Sample thickness, packing density, particle size, refractive

index, crystalline form, surface characteristics 3. Sample scattering coefficient (s) 4. Sample absorption coefficient (k) 5. Measurement geometry 6. Number of detectors (response speed and linearity/dynamic

range) 7. Wavelength of light 8. Polarization effects: s- and p-polarization from beam 9. Beam size and beam angle with respect to sample 10. Sample distance from detector

1. Reflectance and transmittance of window from sample cup

2. Sample thickness and background material

3. Sample scattering coefficient (s) 4. Sample absorption coefficient (k) 5. Measurement geometry 6. Number of detectors (response

speed and linearity/dynamic range) 7. Wavelength of light 8. Polarization effects: s and p-

polarization from beam 9. Beam size, uniformity, and beam

angle with respect to sample 10. Sample distance from detector

1 2, 3, 4

5 5

Illustration

6 6

7, 8

9

10


Sample Thickness and Background Material

Side View

Powder Cup

I0 I

Reflective Back

Window

Sample

2

Change in Percent Reflectance for plane (Rs) and perpendicularly (Rp) polarized

light as a function of the angle of incidence.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 50 100

Ref

lect

ion

Angle of Incidence (Degrees)

Rs

Rp

Φ1 Φ1

Φ2

8

Beam Shape

9

Beam Size vs. Sample Size

1.5 “

9

Main Variability Problem Highlighted:

Distance to Detector

Distance effect: major changes in slope and

offset for each detector in optical path


Sample Window

Detectors

Light Energy – Post-dispersive Front surface Diagonal mirror

Issues Affecting Distance

Sample Layer


B

S0 cos α B cos ϑ

α

ϑ

Sample Holding Device

Sample Window

Angular Distribution of Reflected Light

Sample

0 = Ideal height for maximum reflectance signal amplitude Si

gnal

Am

plit

ud

e

-2 -1 0 +1 +2

Sample Distance from Highest Signal

Sample

+1 (0.0125” or 0.32 mm) Si

gnal

Am

plit

ud

e

-2 -1 0 +1 +2


Sample

+2 (0.0250” or 0.64 mm)

Sign

al A

mp

litu

de

-2 -1 0 +1 +2


Sample

-1 Si

gnal

Am

plit

ud

e

-2 -1 0 +1 +2


-1 (0.0125” or 0.32 mm)

-2

Sample

Sign

al A

mp

litu

de

-2 -1 0 +1 +2


-2 (0.0250” or 0.64 mm)

SN3 Platter

SN2 Platter

Sample in glass cell

Sample only

Instrument #1 With R99

Cup + window = 0.116”

+0.048”

+0.065”

(2.9 mm)

(0 mm)

(1.2 mm)

(1.65 mm)

Sample only

Instrument # 2 With R99

cell = 0.116”Sample in glass cell

(0 mm)

(1.65 mm)

1000 1500 2000 2500

Nanometers

3

4

5

6

Ab

sorb

an

ce

Dark Standard (A~3.2)

Dark Standard (A~3.2) – Diff

1000 1500 2000 2500

Nanometers

-1

0

1

Ab

sorb

an

ce

1000 1500 2000 2500

Nanometers

1.0

1.1

1.2

1.3

Ab

sorb

an

ce

R10 (A~1.0)

0.0 mm

0.32 mm

0.64 mm

R10 (A~1.0) - Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.35

0.40

0.45

0.50

0.55

Ab

sorb

an

ce

R50 (A~0.301)

0.0 mm

0.32 mm

0.64 mm

R50 (A~0.301) - Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

R99 (A~0.0044)

0.0 mm

0.32 mm

0.64 mm

R99 (A~0.0044) – Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.1

0.2

0.3

0.4

0.5

Ab

sorb

an

ce

1920a (A~0.314)

0.0 mm

0.32 mm

0.64 mm

1920a (A~0.314) - Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.2

0.4

0.6

0.8

Ab

sorb

an

ce

Grd. Wheat

0.0 mm

0.32 mm

0.64 mm

Grd. Wheat – Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.2

0.4

0.6

0.8

Ab

sorb

an

ce

Flour

0.0 mm

0.32 mm

0.64 mm

Flour – Diff

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Ab

sorb

an

ce

Forage - Hay

0.0 mm

0.32 mm

0.64 mm

Forage – Hay – Diff.

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

1000 1500 2000 2500

Nanometers

0.03

0.04

0.05

0.06

0.07

Ab

sorb

an

ce

Flour – Wheat – Forage – Diff (1= 0.32 mm)

Flour

Wheat

Forage

Flour – Wheat – Forage – Diff (2= 0.64 mm)

1000 1500 2000 2500

Nanometers

0.12

0.14

0.16

0.18

0.20

0.22

Ab

sorb

an

ce

Flour

Wheat

Forage

R10 – R50 – R99 – Diff (1=0.32 mm)

1000 1500 2000 2500

Nanometers

0.03

0.04

0.05

0.06

Ab

sorb

an

ce

R10 – R50 – R99 – Diff (2=0.64 mm)

1000 1500 2000 2500

Nanometers

0.12

0.14

0.16

0.18

0.20

0.22

Ab

sorb

an

ce

Compare offset distance to Forage multiplied 1.1 and 1.5

1000 1500 2000 2500

Nanometers

0.2

0.4

0.6

0.8

Ab

sorb

an

ce

Superimpose (Normalize) Mode: Compare Forage multiplied 1.1 and 1.5

1000 1500 2000 2500

Nanometers

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

0.25

Ab

sorb

an

ce

Compare offset distance to Forage multiplied 1.1 and 1.5 - Diff

1 Der – 11 pt smooth : Compare Forage multiplied 1.1 and 1.5

1000 1500 2000 2500

Nanometers

-0.015

-0.010

-0.005

0.000

0.005

Abs

orba

nce

1200 1400 1600 1800 2000 2200 2400

Nanometers

0.000

0.002

0.004

0.006

Abs

orba

nce


Close-up

1 Der – 11 pt smooth : Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

-0.010

-0.005

0.000

Abs

orba

nce


1200 1400 1600 1800 2000 2200 2400

Nanometers

-0.001

0.000

0.001

0.002

0.003

0.004

Abs

orba

nce

Close-up

2 Der – 21 pt smooth: Compare Forage multiplied 1.1 and 1.5

Close-up

1200 1400 1600 1800 2000 2200 2400

Nanometers

-0.00010

-0.00005

-0.00000

0.00005

0.00010

Abs

orba

nce

1400 1600 1800 2000 2200 2400

Nanometers

-0.00010

-0.00005

-0.00000

0.00005

0.00010

Abs

orba

nce


Close-up

2 Der – 21 pt smooth: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

-0.0006

-0.0004

-0.0002

0.0000

0.0002

Abs

orba

nce

1000 1200 1400 1600 1800 2000 2200 2400

Nanometers

-0.00010

-0.00005

-0.00000

0.00005

0.00010

Abs

orba

nce


Close-up

Normalize and set minimum to 0 offset: Height and Multiplicative

1000 1500 2000 2500

Nanometers

0.0

0.2

0.4

0.6

Ab

sorb

an

ce

Set mean to zero and then offset min to zero

Normalize and set minimum to 0 offset: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

Ab

sorb

an

ce

Set minimum to 0 offset: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

Ab

sorb

an

ce


1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

Ab

sorb

an

ce

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Ab

sorb

an

ce


1st order poly min to zero

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Ab

sorb

an

ce


2nd order poly (quadratic) min to zero

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

Ab

sorb

an

ce


3rd order poly (quintic) min to zero

1000 1500 2000 2500

Nanometers

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

Ab

sorb

an

ce

Kramers-Kronig: Compare Forage Height Differences

Abs: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Ab

sorb

an

ce

Refl: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Re

fle

cta

nc

e

0.0 mm

0.32 mm

0.64 mm

Kubelka-Munk: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.0

0.5

1.0

1.5

Ku

be

lka

-Mu

nk

0.0 mm

0.32 mm

0.64 mm

Dahm Eq.: Compare Forage Height Differences

0

0.5

1

1.5

2

2.5

3

3.5

4

700 900 1100 1300 1500 1700 1900 2100 2300 2500 2700

0.0 mm

0.32 mm

0.64 mm

Dahm Eq. w offset: Compare Forage Height Differences

0

0.5

1

1.5

2

2.5

3

700 900 1100 1300 1500 1700 1900 2100 2300 2500 2700

0.0 mm

0.32 mm

0.64 mm

Offset min set to zero: Compare Forage Height Differences

1000 1500 2000 2500

Nanometers

0.0

0.1

0.2

0.3

0.4

Ab

sorb

an

ce

Precise Detector Height Alignment Process

Wheat Sample: Five aligned instruments

1000 1500 2000 2500

Nanometers

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Ab

sorb

an

ce

Wheat Sample: Five aligned instruments - Diff

1000 1500 2000 2500

Nanometers

-0.01

0.00

0.01

Ab

sorb

an

ce

Wheat Sample: Five aligned instruments Diff vs height Diff for 1 instrument

1000 1500 2000 2500

Nanometers

0.00

0.05

0.10

0.15

0.20

Ab

sorb

an

ce

0.0 mm

0.32 mm

0.64 mm

Five Instruments

1 instrument

R99-Polystyrene: Five aligned instruments

1000 1500 2000 2500

Nanometers

0.5

1.0

1.5

2.0

2.5

Ab

sorb

an

ce

R99-Polystyrene: Five aligned instruments - Diff

800 1000 1200 1400 1600 1800 2000

Nanometers

-0.02

0.00

0.02

0.04

Ab

sorb

an

ce

SRM1920a: Five aligned instruments

1100 1200 1300 1400

Nanometers

0.1

0.2

0.3

0.4

Ab

sorb

an

ce

Acknowledgments

• John Glaberson, Designs Work Group

• Barry Lavine, Oklahoma State University

• Art Springsteen, Avian Technologies

• Ken Galer, IELLC

• Chris Ubaldi, Unity Scientific

• Bob Schumann, Unity Scientific

• Some of you!

Thank you!

[email protected]

Science

IRDC Theory and practice of building instruments for diffuse reflectance measurements