ASD FieldSpec 3 User manual

FieldSpec® 3 User Manual
ASD Document 600540 Rev. J
© 2010 by ASD Inc.
www.asdi.com

ASD Document 600540 Rev. J ii FieldSpec® 3 User Manual
www.asdi.com
Trademark Information
ASD Inc.
2555 55th Street, Suite 100
Boulder, CO 80301 USA
Phone: [phone]
www.asdi.com
Trademarks FieldSpec®, LabSpec®, QualitySpec®, TerraSpec®,
AgriSpec®, RxSpec®, ViewSpec™, RS3™, Indico™, goLab™, and
HandHeld2™ are registered, and unregistered trademarks, and the intellectual
property of Analytical Spectral Devices, Inc. (dba ASD Inc.). All trademarks
used or displayed in this material are the property of ASD, its affiliates, or
third party owners. Unauthorized use of these trademarks is illegal and
punishable by law. Nothing contained on this Site is to be construed as
granting, by implication, estoppel, or otherwise, any license or right of use of
any such trademark without the prior and express written permission of ASD,
or such third party owner.
This document contains proprietary information protected by copyright law
and may not be reproduced in any manner without the express written
approval of ASD Inc.
The information and specifications contained in this manual are subject to
change without notice. ASD Inc. shall not be held liable for technical,
editorial omissions, or errors made herein; nor for incidental or consequential
damages resulting from furnishing, performance, or use of this material.
Technical Support
If you have any questions or concerns, please contact ASD Inc. by phone, fax,
or email:
Phone: [phone] X-144
Fax: [phone]
email: [email protected]
Web: www.asdi.com
ftp: ftp.asdi.com
Technical support is committed to providing you with a timely response to
your questions. We will work with you to provide solutions to your
applications. Technical support is available to answer your questions Monday
thru Friday, 8 am to 5 pm Mountain Standard Time. We will happily respond
to your e-mail queries as well.

© 2010 ASD Inc. iii FieldSpec® 3 User Manual
Table of Contents
Trademark Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Hardware Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Physical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Power Input and Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
FieldSpec Wavelength Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Interface Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Standard Accessories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Computer Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Software Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Unpacking the Instrument. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Ethernet Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Accessory Power Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Pistol Grip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
External Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Laptop Carrier (Belly Board). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter 3 Usage and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Access and Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Annual Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Returning Instrument to ASD for Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Chapter 4 Fiberoptic Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Fiberoptic Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
LED Check for Fiberoptic Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Fore Optic Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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Chapter 5 Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Battery Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Battery Charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Application Battery Indicator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Chapter 6 Transporting and Carrying the FieldSpec® 3 . . . . . . . . . . . . . . . . . . . . . . . . 41
Packing FieldSpec® 3 for Shipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Preparing the FieldSpec® 3 and Ergonomic Pro-Pack for the Field. . . . . . . 46
Carrying Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Protecting the Instrument in the Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Chapter 7 Field Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Characteristics of Natural Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Characteristics of Artificial Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Atmospheric Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Vegetation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Rocks, Soils, and Man-Made Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Time of Day / Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Sampling Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Viewing Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Suggested Set-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
RS3 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Indico Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
White Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Spectralon Reflectance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Maintaining Spectralon References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
White Reference Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Appendix A Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Common Communication Fixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Does Not Connect to the Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Does Not Connect Wireless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Does Not Connect to the Access Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Spectrometer Loses its Wireless Connection . . . . . . . . . . . . . . . . . . . . . . . . 77
Wireless Interface is Disabled in the Netcfg Application . . . . . . . . . . . . . . . 77

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Appendix B Reference Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Frequently Asked Questions (FAQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
What is a spectroradiometer?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
What are the differences between the ASD spectrometers? . . . . . . . . . 80
What is remote sensing? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
How often do I need to optimize? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
How often do I need a (baseline) White Reference? . . . . . . . . . . . . . . . 81
What spectrum average (or sample count) should I use? . . . . . . . . . . . 81
What if I want to keep the same settings all day? . . . . . . . . . . . . . . . . . 82
When do I use absolute reflectance? . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
How do I know the field-of-view that I’m using? . . . . . . . . . . . . . . . . . . . 82
What are the units of radiance? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Can I post-process my data? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Why do I see oscillations (sine wave) in my data? . . . . . . . . . . . . . . . . . 84
What are these two large noise bands in my data? . . . . . . . . . . . . . . . . 84
What are these upward or downward spikes in VNIR data? . . . . . . . . . 85
What are these steps in my data? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
What can cause more noise in my data from last time? . . . . . . . . . . . . . 86
Why does the VNIR drop to zero after a Dark Current collection? . . . . . 86
How do I collect a reference with a spot size larger than the Spectralon
panel? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
How do I set up GPS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
What does a broken fiber mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
How long is the battery life? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
What type of Ethernet cable can I use for the static IP configuration? . . 89
Can I install additional software on the instrument controller? . . . . . . . . 89
Why does the software seem to do unexpected things? . . . . . . . . . . . . 89
How long does it take for the FieldSpec spectroradiometer to warm up? 90
Where is my serial number?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Data Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Gain and Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Light Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Spectral Discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Field-of-View. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
White Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Other Tips on Discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Spectrum Averaging (or Sample Count). . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

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Temperature Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
W.E.E.E. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

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ASD Document 600540 Rev. J viii FieldSpec® 3 User Manual
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Symbols - Definitions
CAUTION: Risk of danger. This is a personal danger warning.
Documentation must be consulted in all cases where this symbol is marked.
Failure to acknowledge these warnings could result in personal injury to the
user.
CAUTION: Risk of Electric Shock.This is a personal danger warning.
Documentation must be consulted in all cases where this symbol is marked.
Failure to acknowledge these warnings could result in personal injury to the
user.
CAUTION: Hot Surface. This is a personal danger warning. Documentation
must be consulted in all cases where this symbol is marked. Failure to
acknowledge these warnings could result in personal injury to the user.
Recycle. Items with this symbol indicate that the item should be recycled and
not disposed of as general waste.
Warnings and cautions are placed throughout this manual for the convenience
of the reader. However, the absence of warnings and cautions do not preclude
the use of proper caution and handling. Usual precautions are recommended
to be taken at all times, either written or otherwise, to avoid personal injury or
damage to ASD equipment.

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The Power Supply is intended for Indoor Use Only
When using an electrical appliance, basic safety precautions should always be
followed.
Danger- To reduce the risk of electric shock read all instructions before using
the power supply. A power supply should never be left unattended when
plugged in. Always unplug the power supply from the mains socket
immediately after using.
Warning- To reduce risk of burns, fire, electric shock or injury to persons or
animals:
1. Use this power supply only for its intended use as described below.
2. Do not use outdoors.
3. Do not allow to be used as a toy. Pay close attention when this power
supply is used by, or near to, children.
4. Use only attachments recommended by the manufacturer.
5. Never operate the power supply if it has a damaged cord or plug, if it has
been dropped or damaged or if it has fallen into water. In such cases return the
power supply to an authorized dealer or service center for examination or
repair.
6. Never drop or insert an object into any openings.
7. Do not operate where aerosol (spray) products are being used or where
oxygen is being administered.
8. The power supply should be used near to a convenient and easily accessible
mains socket.

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Notes:

© 2010 ASD Inc. 1 FieldSpec® 3 User Manual
Chapter 1 Introduction
The FieldSpec® 3 Spectroradiometer is a general-purpose spectrometer
useful in many application areas requiring the measurement of reflectance,
transmittance, radiance, or irradiance.
•Aspectrometer is an optical instrument that uses detectors other than
photographic film to measure the distribution of radiation in a particular
wavelength region.
•Aspectroradiometer is a special kind of spectrometer that can measure
radiant energy (radiance and irradiance.) Unlike other ASD
spectrometers, the FieldSpec instrument can perform radiance
measurements by default coming from the factory, because its Fiberoptic
cable is fixed.
Note: The Fiberoptic cable significantly affects the factory calibration
required to measure radiance. Many of the other ASD
spectrometers can detach and even interchange Fiberoptic cables,
which can affect the accuracy of such calibrated radiance
measurements.
The FieldSpec spectroradiometer is specifically designed for field
environment remote sensing to acquire visible near-infrared (VNIR) and
short-wave infrared (SWIR) spectra. Remote sensing is defined as the art and
science of obtaining information about an object without being in direct
physical contact with the object.
The FieldSpec spectroradiometer is a compact, field portable, and precision
instrument with a spectral range of 350-2500 nm and a rapid data collection
time of 0.1 second per spectrum. The FieldSpec spectroradiometer is also
offered in various subsections of the spectral range.
While the most highly regarded features of the FieldSpec spectroradiometer
are performance and field-portability, this instrument also performs well in
the laboratory.

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Features and Advantages
Accurate and Precise - High signal-to-noise ratio and superior
repeatability of results for better identification and analysis of materials.
Rugged and Transportable - Resistant to vibration and changes in
temperature or humidity.
Fast - 10 spectra per second data collection for the entire 350-2500 nm range.
»0.1second scanning time provides an accurate average every second.
» Users can quickly scan several areas when analyzing bulk samples.
» Rapid analysis allows screening all or most samples instead of spot
checking.
Compatible - Works with off-the-shelf chemometrics software
(Grams™ PLS plus/IQ and Unscrambler®).
1.1 Hardware Specifications
This section contains details about the FieldSpec spectroradiometer.
1.1.1 Physical Specifications
•Durable satin powder coat finish with teal urethane end-caps and handles
•All vital components are in a dust-proof enclosure and EMI sealed
• Fiberoptic inputs directly to each spectrometer
Height 12.7 cm 5 inches
Width 35.6 cm 14.5 inches
Depth 29.2 cm 11.5 inches
Weight 5.6 kg 12 lbs

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1.1.2 Power Input and Output
The near infrared (NIR) is also called the short-wave infrared (SWIR).
1.1.3 FieldSpec Wavelength Configuration
AC Power Supply Type Auto ranging, Switching, SELV
AC Input 90-240 VAC, 50/60 Hz
DC Input +12 VDC, 60 W
Accessory Power Port 
(front of instrument)
Output, +12 VDC, 27 Watt (max).
Instrument Configuration Power Rating Maximum
350-1050nm 12 VDC, 45 Watt
350-1800nm 12 VDC, 50 Watt
1000-1800nm 12VDC, 50 Watt
1800-2500nm 12 VDC, 50 Watt
1000-2500nm 12 VDC, 60 Watt
350-2500nm 12 VDC, 60 Watt
Wavelength Name Wavelength Range
VNIR-SWIR1-SWIR2 350 - 2500 nm
VNIR only 350 - 1050 nm
VNIR-SWIR1 350 - 1800 nm
SWIR1 only 1000 - 1800 nm
SWIR1-SWIR2 1000 - 2500 nm
SWIR2 only 1800 - 2500 nm
VNIR & SWIR2 350 - 1050 nm and 1800 - 2500 nm

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The spectral resolution is:
•3nm (Full-Width-Half-Maximum) at 700 nm.
•10 nm (Full-Width-Half-Maximum) at 1400 nm.
•10nm (Full-Width-Half-Maximum) at 2100 nm.
The sampling interval is:
•1.4nm for the spectral region 350-1000 nm.
•2nm for the spectral region 1000-2500 nm.
The FieldSpec spectroradiometer may be configured to have three separate
holographic diffraction gratings with three separate detectors. Each detector is
also covered with the appropriate order separation filters to eliminate second
and higher order light.
•VNIR: 512 element silicon photo-diode array for the spectral region
350-1000 nm.
• SWIR1: graded index, TE-cooled, extended range, InGaAs, photo-diode
for the spectral region 1000 nm to 1830 nm.
• SWIR2: graded index, TE-cooled, extended range, InGaAs, photo-diode
for the spectral region 1830 nm to 2500 nm.
1.1.4 Interface Requirement
The FieldSpec spectroradiometer has 10/100 Base T Ethernet port. The
spectroradiometer with an Ethernet cross-over cable can be directly connected
to the Ethernet port provided on many laptop computers.
The FieldSpec spectroradiometer can communicate with the instrument
controller using an 802.11b wireless card. When supplied by the customer, the
instrument controller must be 802.11b compatible.
The FieldSpec spectroradiometer uses industry standard components. It has
the same general connection speed and distance capabilities as other 802.11b
wireless devices.
For the best performance, ensure a clear line-of-sight between the
spectroradiometer and instrument controller. Obstructions or radio frequency
interference in close proximity can cause loss of communication or
significantly shorten the communication range.
Note: For information about configuration of the Ethernet card and cable, please
refer to the Installation Manual.

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1.1.5 Standard Accessories
• FieldSpec® 3 Spectroradiometer
• FieldSpec® 3 User Manual (PDF on Flash Drive)
•Instrument Controller: ASD-approved laptop computer
•RS3Software Pack
•1.5 meter FR Low OH Fiberoptic Cable
•Power Supply 12 V
•NiMh Battery (12 V, 9000 mA hour) with Charger and 6 ft.
Battery-to-instrument Power Cable
•Power Adapter with 6 m (20 ft) Cable for Automobile Cigarette Lighter
When using this adapter, turn off the vehicle engine. Electromagnetic
fields from the engine can generate noise in the acquired signals.
•1.5meter Instrument-to-Probe Accessory Power Cable
• Remote Trigger with LEDs and Velcro Pads
•RJ45 CAT 5e UTP Ethernet, Shielded, Crossover Cable
•64MB (min.) Flash Drive Memory USB Flash Drive
• Mylar Wavelength Reference
•FieldSpec Pistol Grip
• Laptop Carrier (Belly Board) Equipped with Pistol Grip Holder
• Ergonomic Pro-Pack with built-in rain protector, sample storage
compartment, instrument controller (laptop) compartment, and two
battery pouches designed for the hip belt
•Magnifier for Fiber Checker
•Shipping Trunk: Durable, air tight, wheeled, fold down handle, and foam
filled with cutouts to protect the instrument and many accessories

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1.2 Computer Requirements
The instrument controller is a computer that manages the FieldSpec
spectroradiometer, stores data, and processes the results.
The standard FieldSpec spectroradiometer includes a laptop computer, or the
instrument controller.
The minimum requirements for the instrument controller are:
•1.2GHz Pentium or better notebook or PC-w/monitor
•256MB RAM or more
•20GB of free disk space
• 1024 x 768 or better graphics resolution
• 24-bit color or better - 32-bit recommended
•Ethernet port: 10/100 Base T Ethernet interface
•(Optional) Ethernet wireless (WiFi) adaptor: PCMIA, USB, or built-in
that is compatible with the 802.11b standard
•(Optional) Serial communications port (or USB port) for GPS receiver
(only needed if you want to use GPS)
• (Optional) NMEA compatible GPS receiver
1.3 Software Requirement
The instrument controller requires the following software:
•RS3Software from ASD
•Microsoft Windows® 95/98/NT/2000/ME/XP Operating System
• Microsoft Internet Explorer 6.0 or better
Users need a basic understanding of the Microsoft Windows operating system
including software installation.
International customers using non-English versions of Windows must alter
the Regional Settings under Start->Settings->Control Panel. The
default language must be set to English (United States) in order for the
software to be registered and operate correctly. The numbering format must
also be set to English.

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1.4 Theory of Operation
The FieldSpec spectroradiometer measures the optical energy that is reflected
by, absorbed into, or transmitted through a sample. Optical energy refers to a
wavelength range that is greater than just the visible wavelengths, and is
sometimes called electromagnetic radiation or optical radiation.
In its most basic configuration, the spectroradiometer views and detects the
form of radiant energy defined as radiance. With accessories, various set-ups,
and built-in processing of the radiance signal, the FieldSpec
spectroradiometer can measure:
• spectral reflectance,
• spectral transmittance,
• spectral absorbance,
• spectral radiance, and
• spectral irradiance.
Fiberoptic Collection of Reflected/Transmitted Light
Optical energy is collected through a bundle of specially formulated optical
fibers, precisely cut, polished, and sealed for extremely efficient energy
collection. The fibers themselves are of low OH composition providing the
maximum transmission available across the wavelength range of the
instrument.
Inside the FieldSpec® 3 Spectroradiometer
The fiber cable delivers the collected optical energy into the instrument,
where it is projected onto a holographic diffraction grating. The grating
separates and reflects the wavelength components for independent
measurement by the detectors.
Visible/Near-Infrared (VNIR)
The Visible/Near-Infrared (VNIR: 350-1000 nm wavelength) portion of the
spectrum is measured by a 512-channel silicon photodiode array overlaid with
an order separation filter. Each channel (or detector) is geometrically
positioned to receive light within a narrow (1.4 nm) range. The VNIR
spectrometer has a spectral resolution (full-width half maximum of a single
emission line) of approximately 3 nm at around 700 nm.
Each detector converts incident photons into electrons. This photo current is
continually converted to a voltage and is then periodically digitized by a
16-bit analog-to-digital (A/D) converter. This digitized spectral data is then
transmitted to the instrument controller for further processing and analysis by
the controlling software.

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The 512-channel array permits the entire VNIR spectrum to be scanned in
parallel at 1.4 nm wavelength intervals. A single sample can be acquired in as
little as 17 ms.
Short-Wave Infrared (SWIR)
The Near-Infrared (NIR), also called Short-Wave Infrared (SWIR), portion of
the spectrum is acquired with two scanning spectrometers:
•SWIR1 for the wavelength range of 1000 nm to 1830 nm
• SWIR2 for the wavelength range of 1830 nm to 2500 nm
The SWIR scanning spectrometers have one detector for SWIR1 and another
for SWIR2. This is different from the VNIR spectrometer, which has an array
of 512 detectors. Thus, SWIR spectrometers collect wavelength information
sequentially rather than in parallel.
Each SWIR spectrometer consists of a concave holographic grating and a
single thermo-electrically cooled Indium Gallium Arsenide (InGaAs)
detector. The gratings are mounted around a common shaft that oscillates
back and forth through a 15 degree swing. As the grating moves, it exposes
the SWIR1 and SWIR2 detectors to different wavelengths of optical energy.
Each SWIR spectrometer has ~600 channels, or ~2 nm sampling interval per
SWIR channel. The spectroradiometer firmware automatically compensates
for the overlap in wavelength intervals.
Like the VNIR detectors, the SWIR1 and SWIR2 detectors convert incident
photons into electrons. This photo current is continually converted to a
voltage and is then periodically digitized by a 16-bit analog-to-digital (A/D)
converter. This digitized spectral data is then transmitted to the instrument
controller for further processing and analysis by the controlling software.
The grating is physically oscillating with a period of 200 ms. It performs a
forward scan and a backward scan, resulting in 100 ms per scan. This is the
minimum time required for any SWIR samples, or full-range samples.
Communicating with the Instrument Controller (Computer)
The FieldSpec spectroradiometer communicates with the instrument
controller using a cross-over Ethernet cable or Wireless Ethernet (WiFi)
interface. The amount of data that is sent depends on the configuration of the
spectroradiometer.
•A single sample of VNIR is ~1024 bytes
• A single sample of SWIR1 is ~2400 bytes
• A single sample of SWIR2 is ~2400 bytes
A full-range FieldSpec spectroradiometer can create packet data sizes over
5KB. Other single or dual range configurations of the spectroradiometer
create smaller data packets (adding the packet sizes as above.)

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When features for spectrum averaging (or sample count) are turned on within
the application software on the instrument controller, the averaging is
performed at the spectroradiometer.
Dark Current Measurement
Dark Current (DC) refers to current generated within a detector in the absence
of any external photons. DC is the amount of electrical current that is inherent
in the spectrometer’s detectors and other electrical components and is additive
to the signal generated by the measured external optical radiation.
Note: Noise is the uncertainty in a given measurement, one channel at a time. Noise
by definition is random. Noise can be reduced by using more samples and
averaging the signal. Dark Current is different from noise, because it is
relatively stable and can be characterized.
This manual uses DC to refer to all systematic contributions to the detector
signal. DC is a property of the detector and the associated electronics (not the
light source). DC varies with temperature. In the VNIR region, DC also varies
with integration time.
Whenever DC is taken, a mechanical shutter is used to block off the entrance
slit of the VNIR spectrometer so the signal can be measured. This signal is
subtracted from each subsequent spectrum until another DC is taken. The
SWIR spectrometers take and subtract DC on every scan.
The DC measurement can be updated at any time, but should be updated more
frequently in the beginning of a given session while the instrument warms up.
The VNIR spectrometer is fitted with a unique software and hardware
combination feature called Driftlock. Driftlock corrects for DC changes over
time. It automatically updates DC for every measurement by looking at a
series of masked pixels at the front portion of the VNIR array. The Driftlock
feature corrects for the majority of DC variation over time.
White Reference
A material with approximately 100% reflectance across the entire spectrum is
called a white reference panel or white reference standard.
The raw measurement made by the spectroradiometer is influenced by both
the sample and the light source. An independent measure of the light source
illumination on a reference of known reflectance is required to calculate the
reflectance of the sample. The use of a white reference standard with near
100% reflectance simplifies this calculation.
Reflectance and transmittance are inherent properties of all materials and are
independent of the light source.
Reflectance is the ratio of energy reflected from a sample to the energy
incident on the sample. Spectral Reflectance is the reflectance as a
function of wavelength.

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Transmittance is the ratio of the radiant energy transmitted through a sample
to the radiant energy incident on the surface of the sample. Spectral
Transmittance is the transmittance as a function of wavelength.
Relative reflectance is computed by dividing the energy reflected from the
sample by the energy reflected off a white reference panel or standard.
Absolute reflectance is computed by multiplying the relative reflectance by
the known reflectance of the white reference panel.
With the reflectance of the reference standard available and known, the ASD
RS3or Indico applications can compute the absolute reflectance or
transmittance for the material being sampled.
Accessories for Light Sources and Probes
ASD offers several accessories for:
• Delivering illumination to the sample.
• Collecting reflected or transmitted light from the sample.
•Collecting reflected or transmitted radiance and irradiance from the
sample (where solar light is the primary source of illumination).
• Transmitting the collected light to the spectrometer.
Some accessories, such as many of the optional foreoptic probes, rely on other
illumination sources, and even solar light.