Decagon Devices SRS Bedienungsanleitung

SRS

Spectral Reﬂectance Sensor

Operator’s Manual

Decagon Devices, Inc.

Version: January 15, 2014 — 12:16:45

SRS Sensors

Decagon Devices, Inc.

2365 NE Hopkins Court

Pullman WA 99163

Phone: 509-332-5600

Fax: 509-332-5158

Website: www.decagon.com

Email: supp[email protected] or [email protected]

Trademarks

2007-2013 Decagon Devices, Inc.

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 Fractional Interception of Photosynthetically Active

Radiation ......................... 8

3.3 Canopy Phenology . . . . . . . . . . . . . . . . . . . . 10

3.4 Photochemical Reﬂectance Index (PRI) . . . . . . . . 11

3.5 Sun-Sensor-Surface Geometry Considerations . . . . . 12

3.6 Calculating Percent Reﬂectance from Paired Up and

Down Looking Sensors . . . . . . . . . . . . . . . . . . 14

4 Connecting the SRS 19

4.1 Connecting to Decagon Data Logger . . . . . . . . . . 19

4.2 3.5 mm Stereo Plug Wiring . . . . . . . . . . . . . . . 20

4.3 Connecting to a Non-Decagon Logger . . . . . . . . . 20

4.4 Pigtail End Wiring . . . . . . . . . . . . . . . . . . . . 21

5 Communication 23

5.1 SDI-12 Communication . . . . . . . . . . . . . . . . . 23

6 Understanding Data Outputs 25

6.1 Using Decagon’s Em50 series data loggers . . . . . . . 25

6.1.1 Up Looking Sensor Outputs . . . . . . . . . . . 25

6.1.2 Down Looking Sensor Outputs . . . . . . . . . 25

6.2 Using other data loggers . . . . . . . . . . . . . . . . . 26

7 Installing the SRS 27

7.1 Attaching and Leveling . . . . . . . . . . . . . . . . . 27

7.2 Cleaning and Maintenance . . . . . . . . . . . . . . . . 27

iii

CONTENTS SRS Sensors

8 Troubleshooting 28

8.1 DataLogger........................ 28

8.2 Sensors .......................... 28

8.3 Calibration ........................ 28

9 Declaration of Conformity 29

SRS Sensors 1 INTRODUCTION

1 Introduction

Thank you for choosing Decagon’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 it to be low cost, easily

and quickly deployable, and capable of reliable operation over years.

Deploy the sensors over plant canopies to record ﬁrst appearance of

green canopy, canopy closure, canopy senescence, light use eﬃciency,

and other variables. Customers can use these measurements to de-

termine light capture, water use, phenology and biomass production.

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. Decagon has Cus-

tomer Service Representatives available to speak with you Monday

through Friday, between 7am and 5pm Paciﬁc time.

Note: If you purchased your sensor through a distributor, please con-

tact them for assistance.

Email:

supp[email protected] or [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.

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 con-

stitutes Buyer’s acceptance of the terms set forth in this warranty.

There are no understandings, representations, or warranties of any

kind, express, implied, statutory or otherwise (including, but with-

out limitation, the implied warranties of merchantability and ﬁtness

for a particular purpose), not expressly set forth herein.

SRS Sensors 2 ABOUT SRS

2 About SRS

2.1 Overview

The SRS are two-band radiometers that measure either incident or

reﬂected radiation in wavelengths appropriate for calculating the

Normalized Diﬀerence Vegetation Index (NDVI) or the Photochemi-

cal Reﬂectance Index (PRI). Sensors are manufactured in four diﬀer-

ent versions: NDVI-hemispherical, NDVI-ﬁeld stop, PRI-hemispherical

and PRI-ﬁeld stop. The hemispherical versions (Figure 1) are built

with Teﬂon diﬀusers for making cosine-corrected measurements, and

are primarily designed for up looking measurements of incident radi-

ation. The ﬁeld stop versions (Figure 2) have a ﬁeld of view restricted

to 20◦and are designed for pointing downward to measure canopy

reﬂected radiation in NDVI and PRI wavelengths.

The reﬂected radiation from a vegetated surface is highly variable,

depending on the amount and type of vegetation cover. This vari-

ability requires a relatively large number of sensors to properly char-

acterize this surface. The ﬁeld stop and hemispherical versions can

both be used to quantify canopy reﬂected radiation. The correct

choice of sensor will depend on the objectives of the study. The

hemispherical sensor will do a better job of averaging reﬂected radia-

tion over a broad area, but if it is not installed normal to the canopy

surface it will also average sky, leading to measurement error. The

ﬁeld stop sensor can be aimed at a particular spot or have a particu-

lar orientation giving the user more control over what portion of the

canopy is being measured. When using the ﬁeld stop sensor in an

oﬀ-nadir orientation the user should be careful that the sensor is not

pointed above the horizon.

Calculating NDVI or PRI requires knowing both the incoming and

reﬂected radiation. Unlike the reﬂected radiation, the incoming radi-

ation is spatially uniform above the canopy. So, you only need one up

facing radiometer to compute the vegetation indices for many down

facing radiometers. The up looking radiometer should be leveled and

have a hemispherical ﬁeld of view.

2 ABOUT SRS SRS Sensors

The SRS is a digital sensor. Its outputs follow the SDI-12 stan-

dard. The SRS is best suited for use with Decagon’s Em50, Em50R,

and Em50G data loggers. However, customers can use the SRS with

other loggers, such as those from Campbell Scientiﬁc.

Figure 1: Hemispherical Version Figure 2: Field Stop Version

2.2 Speciﬁcations

Accuracy: 10% or better for spectral irradiance and radiance values

Measurement Time: <300 ms

NDVI Wavebands: 630 and 800 nm central wavelengths, with 50

and 40 nm full width half maximum band widths

PRI Wavebands: 531 and 571 nm central wavelengths, with 10 nm

full width half maximum band widths

Dimensions: 43 x 40 x 27 mm

Power Requirements: 3.6 to 15 V DC, 4 mA (reading, 300 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; custom cable length available upon

request.

SRS Sensors 2 ABOUT SRS

Other Features:

•SDI-12 digital sensor, compatible with Decagon’s EM50

family and CSI loggers

•In-sensor storage of calibration values

•Four versions

NDVI-hemispherical

NDVI-ﬁeld stop

PRI-hemispherical

PRI-ﬁeld stop

•NDVI or PRI sensors with Teﬂon cosine correcting heads

•NDVI or PRI sensors with 20 degree ﬁeld stops sealed

with clear acrylic

•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

•Fully sealed from the elements and UV resistant to mini-

mize drift over time

3 THEORY SRS Sensors

3 Theory

Decagon designed the SRS instruments to measure the NDVI and

PRI vegetation indices from plant canopies. We caution users that

NDVI and PRI are measurements of electromagnetic radiation re-

ﬂected from canopy surfaces, and therefore provide indirect or cor-

relative 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 uncovered. While NDVI and PRI can be powerful

tools for inferring structure and function of plant canopies, you must

take into account their limitations when interpreting the data. Sec-

tion 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 of the most common nonde-

structive techniques involves measuring the NDVI. The NDVI is one

of a large number of vegetation indices. The principle 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,

but are highly reﬂective in the near infrared region (Figure 3). Be-

cause bare soil, detritus, stems, trunks, branches, and other non-

photosynthetic elements show relatively little diﬀerence in reﬂectance

between the visible and near infrared, measuring the diﬀerence be-

tween reﬂectance in these two bands can be related to the amount

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