METER Group, Inc. Spectral Reflectance Sensor Manuale utente
SRS
Spectral Reflectance Sensor
Operator’s Manual
METER Group, Inc. USA
14597-02
SRS Sensors
METER Group, Inc. USA
2365 NE Hopkins Court
Pullman WA 99163
Phone: 509-332-5600
Fax: 509-332-5158
Website: www.metergroup.com
sales.environmen[email protected]
METER Group, Inc. USA
c
2006-2019
All Rights Reserved
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SRS Sensors CONTENTS
Contents
1 Introduction 1
1.1 Customer Support . . . . . . . . . . . . . . . . . . . . 1
1.2 About This Manual . . . . . . . . . . . . . . . . . . . 2
1.3 Warranty ......................... 2
1.4 Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . 2
2 About SRS 3
2.1 Overview ......................... 3
2.2 Specifications ....................... 4
3 Theory 6
3.1 Normalized Difference Vegetation Index (NDVI) . . . 6
3.2 EstimatingLAI...................... 8
3.3 Fractional Interception of Photosynthetically Active
Radiation ......................... 8
3.4 Canopy Phenology . . . . . . . . . . . . . . . . . . . . 10
3.5 Photochemical Reflectance Index (PRI) . . . . . . . . 11
3.6 Sun-Sensor-Surface Geometry Considerations . . . . . 12
3.7 Calculating Percent Reflectance from Paired Up and
Down Looking Sensors . . . . . . . . . . . . . . . . . . 15
4 Field Installation 19
5 Connecting the SRS 21
5.1 Connecting to METER Data Logger . . . . . . . . . . 21
5.2 3.5 mm Stereo Plug Wiring . . . . . . . . . . . . . . . 22
5.3 Connecting to a Non-METER Logger . . . . . . . . . 22
5.4 Pigtail End Wiring . . . . . . . . . . . . . . . . . . . . 23
6 Communication 25
6.1 SDI-12 Communication . . . . . . . . . . . . . . . . . 25
7 Understanding Data Outputs 27
7.1 Using METER’s Data Loggers . . . . . . . . . . . . . 27
7.1.1 Up Looking Sensor Outputs . . . . . . . . . . . 27
7.1.2 Down Looking Sensor Outputs . . . . . . . . . 27
7.2 Using other data loggers . . . . . . . . . . . . . . . . . 28
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CONTENTS SRS Sensors
8 Installing the SRS 29
8.1 Attaching and Leveling . . . . . . . . . . . . . . . . . 29
8.2 Cleaning and Maintenance . . . . . . . . . . . . . . . . 29
9 Troubleshooting 31
9.1 DataLogger........................ 31
9.2 Sensors .......................... 31
9.3 Calibration ........................ 31
10 Declaration of Conformity 33
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SRS Sensors 1 INTRODUCTION
1 Introduction
Thank you for choosing METER’s Spectral Reflectance Sensor (SRS).
We designed the SRS for continuous monitoring of Normalized Differ-
ence Vegetation Index (NDVI) and/or the Photochemical Reflectance
Index (PRI) of plant canopies. We intend for the SRS to be low cost,
easily and quickly deployable, and capable of reliable operation over
years. NDVI and PRI are used by researchers to monitor canopy
biomass, leaf area, phenology (green up and senescence), biomass
production, and light use efficiency, among other variables. This
manual will help you understand the sensor features and how to use
this device successfully.
1.1 Customer Support
If you ever need assistance with your sensor, have any questions or
feedback, there are several ways to contact us. METER has Cus-
tomer Service Representatives available to speak with you Monday
through Friday, between 7 am and 5 pm Pacific time.
Note: If you purchased your sensor through a distributor, please con-
tact them for assistance.
Email:
sales.environmen[email protected]
Phone:
509-332-5600
Fax:
509-332-5158
If contacting us by email or fax, please include as part of your mes-
sage your instrument serial number, your name, address, phone, fax
number, and a description of your problem or question.
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1 INTRODUCTION SRS Sensors
1.2 About This Manual
Please read these instructions before operating your sensor to ensure
that it performs to its full potential.
1.3 Warranty
The sensor has a 30-day satisfaction guarantee and a one-year war-
ranty on parts and labor. Your warranty is automatically validated
upon receipt of the instrument.
1.4 Seller’s Liability
Seller warrants new equipment of its own manufacture against de-
fective workmanship and materials for a period of one year from the
date of receipt of equipment.
Note: We do not consider the results of ordinary wear and tear,
neglect, misuse, or accident as defects.
The Seller’s liability for defective parts shall in no event exceed the
furnishing of replacement parts “freight on board” the factory where
originally manufactured. Material and equipment covered hereby
which is not manufactured by Seller shall be covered only by the
warranty of its manufacturer. Seller shall not be liable to Buyer for
loss, damage or injuries to persons (including death), or to property
or things of whatsoever kind (including, but not without limitation,
loss of anticipated profits), occasioned by or arising out of the instal-
lation, operation, use, misuse, nonuse, repair, or replacement of said
material and equipment, or out of the use of any method or process
for which the same may be employed. The use of this equipment
constitutes Buyer’s acceptance of the terms set forth in this war-
ranty. There are no understandings, representations, or warranties
of anykind, express, implied, statutory or otherwise (including, but
without limitation, the implied warranties of merchantability and
fitness for a particular purpose), not expressly set forth herein.
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SRS Sensors 2 ABOUT SRS
2 About SRS
2.1 Overview
The SRS are two-band radiometers we designed to measure either in-
cident or reflected radiation in wavelengths appropriate for calculat-
ing the Normalized Difference Vegetation Index (NDVI) or the Pho-
tochemical Reflectance Index (PRI). They are designed to be an al-
ternative to more complex and costly spectrometers. The SRS sensor
comes in four different versions: NDVI-hemispherical (Ni), NDVI-
field stop (Nr), PRI-hemispherical (Pi) and PRI-field stop (Pr). The
hemispherical versions (Figure 1) are built with Teflon diffusers for
making cosine-corrected measurements, with a hemispherical 180◦
FOV, and are primarily designed for up looking measurements of in-
cident radiation. The field stop versions (Figure 2) have a field of
view restricted to 36◦(18◦half angle) and are designed for pointing
downward to measure canopy reflected radiation.
Calculating NDVI or PRI requires knowing both incoming and re-
flected radiation. Unlike the reflected radiation, the incoming radia-
tion is spatially uniform above the canopy. So, you only need one up
facing radiometer to compute the vegetation indices for many down
facing radiometers that are within the same general area. The up
looking radiometer must be leveled and have a hemispherical field of
view.
The SRS is a digital sensor. Its outputs follow the SDI-12 standard.
The SRS is best suited for use with METER’s data loggers. How-
ever, customers can use the SRS with other loggers, such as those
from Campbell Scientific.
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2 ABOUT SRS SRS Sensors
Figure 1: Hemispherical Version Figure 2: Field Stop Version
2.2 Specifications
Accuracy: 10% or better for spectral irradiance and radiance values
Measurement Time: <600 ms
NDVI Wavebands: 650 and 810 nm central wavelengths, with 10
nm full width half maximum band widths
PRI Wavebands: 532 and 570 nm central wavelengths, with 10 nm
full width half maximum band widths
Field of View: Hemispherical version: 180◦full angle, Field stop
version: 36◦full angle (18◦half angle)
Dimensions: 43 x 40 x 27 mm
Weight: 47 g (sensor), 170 g (sensor with 5 m cable)
Power Requirements: 3.6 to 15 V DC, 4 mA (reading, 600 ms) 30
µA (quiescent)
Operating Temperature: −40 to 50 ◦C
Connector Types: 3.5 mm (stereo) plug or stripped & tinned lead
wires (Pigtail)
Cable Length: 5 m standard
Other Features:
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SRS Sensors 2 ABOUT SRS
•SDI-12 digital sensor, compatible with METER data log-
gers and CSI loggers
•In-sensor storage of calibration values
•Four versions
Ni - NDVI hemispherical
Nr - NDVI field stop
Pi - PRI hemispherical
Pr - PRI field stop
•NIST traceable calibration to known spectral radiance or
irradiance values
•Sensors can be mounted facing up or down, singly or in
tandem, leveled or aimed
•Sensor body and electronics are fully sealed from the ele-
ments and UV resistant to minimize drift over time
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3 THEORY SRS Sensors
3 Theory
METER designed the SRS to measure NDVI and PRI vegetation in-
dices from plant canopies. We caution users that NDVI and PRI are
derived from measurements of radiation reflected from canopy sur-
faces, and therefore provide only indirect or correlative associations
with several canopy variables of interest and should not be treated
as direct measurements of these variables.
NDVI has a well-established and long history of use in remote sens-
ing research and ecological applications related to canopy structure.
PRI, while showing great promise for quantifying canopy physiolog-
ical function, is far more experimental with new uses and caveats
continually being discovered. While NDVI and PRI can be power-
ful tools for inferring structure and function of plant canopies, you
must take into account their limitations when interpreting the data.
Section 3 provides an overview of the theory and discusses some of
the uses and limitations of each vegetation index.
3.1 Normalized Difference Vegetation Index (NDVI)
A number of nondestructive methods exist for remotely monitoring
and quantifying certain canopy characteristics. Some of those char-
acteristics are: foliar biochemistry and pigment content, leaf area
index (LAI, Nguy-Robinson et al., 2012), phenology, and canopy
photosynthesis (Ryu et al., 2010). One nondestructive method in-
volves measuring NDVI. The underlying principle of NDVI derives
from a well known concept that vegetation reflects light differently in
the visible spectrum (400 to 700 nm) compared to the near infrared
(>700 nm).
Green leaves absorb light most strongly in the visible spectrum, es-
pecially at red wavelengths, but are highly reflective in the near in-
frared region (Figure 3). Because bare soil, detritus, stems, trunks,
branches, and other non-photosynthetic elements show relatively lit-
tle difference in reflectance between the visible and near infrared,
measuring the difference between reflectance in these two bands can
be related to the amount green vegetation in the field of view of a ra-
6
Indice
