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METER Group, Inc. Spectral Reflectance Sensor, Operator'S Manual

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SRS Sensors

4

FIELD INSTALLATION

4

Field Installation

The SRS is designed to be light weight, weatherproof, consume low
power, and have a small size so that it can be deployed virtually
anywhere with relative ease. Because the SRS measures incident
and reflected radiation it must be mounted above the plant canopy.
For example, the SRS can be mounted to a post, pole, tripod, tower,
or other similar infrastructure that extends above the canopy. When
measuring incident radiation with a hemispherical view SRS, be sure
that the sensor’s view of the sky is unobstructed. This is easiest
done by placing the sensor above the canopy, however, it may also be
achieved by placing the hemispherical sensor in a large canopy gap or
forest clearing. Field stop sensors should also generally be mounted
above a canopy, but there may be instances where an oblique or
side-view of a canopy is more practical than trying to get the sensor
above the top of the canopy.

The field stop and hemispherical versions can both be used to quan-
tify canopy reflected radiation.

The correct choice of sensor will

depend on the objectives of the study. The hemispherical sensor
has a ground instantaneous field of view (GIFOV) of 180

◦

(full an-

gle), and will do a better job of averaging reflected radiation over a
broad area. When using hemispherical view sensors in a down-facing
orientation, extreme care should be taken to mount the sensor per-
fectly horizontal so that the sensor does not ”see” any sky above the
horizon. The field stop sensor can be aimed at a particular spot or
have a particular 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.

For most applications the field stop SRS is the most appropriate
sensor for acquiring down-facing measurements because it allows for
more control of the measurement area. For example, in an open
canopy woodland, the field stop sensor can be directed at a tree

19

Summary of Contents for Spectral Reflectance Sensor

Page 1: ...SRS Spectral Reflectance Sensor Operator s Manual METER Group Inc USA 14597 02 ...

Page 2: ...2365 NE Hopkins Court Pullman WA 99163 Phone 509 332 5600 Fax 509 332 5158 Website www metergroup com Email support environment metergroup com or sales environment metergroup com METER Group Inc USA c 2006 2019 All Rights Reserved ii ...

Page 3: ...chemical 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 Un...

Page 4: ...S SRS Sensors 8 Installing the SRS 29 8 1 Attaching and Leveling 29 8 2 Cleaning and Maintenance 29 9 Troubleshooting 31 9 1 Data Logger 31 9 2 Sensors 31 9 3 Calibration 31 10 Declaration of Conformity 33 iv ...

Page 5: ...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 throug...

Page 6: ...ard 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 arisi...

Page 7: ...rily 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 ...

Page 8: ...s 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 ster...

Page 9: ...ions 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 5 ...

Page 10: ...nd 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 201...

Page 11: ...erence between reflectance spectra from the soil and all stages of plant development Second the changes in the visible spectra as the canopy matures and senesces Figure reproduced with permission from Royo and Dolors 2011 Calculate NDVI as NDV I ρNIR ρred ρNIR ρred 1 where ρred and ρNIR are percent reflectances in the red and near infrared NIR We assume percent reflectance to be the ratio of refle...

Page 12: ...tween the two crops but not identical These relationships have been developed for a wide range of crop and natural canopies and we encourage our customers to seek out the best relationship for their application Figure 4 Relationship between leaf area index and NDVI for 20 25 durum wheat genotypes studied over two years in seven different experiments by Aparicio et al 2002 Values shown were taken a...

Page 13: ...ed sensitivity when LAI is high shaded leaves tend to have much less impact on light capture com pared to sunlit leaves and therefore contribute proportionally less to canopy productivity As a general modeling parameter an estimate of sunlit leaves may be adequate for estimating photosynthesis and biomass accumulation i e carbon uptake for some applications Monteith 1977 proposed the now well know...

Page 14: ... variables are the focus of Ryu et al 2010 who used an NDVI sensor similar to the SRS NDVI to measure canopy phenology and associated changes in photosynthesis in an annual grassland over a four year period Ryu et al 2010 show an exponential relationship between NDVI and canopy photo synthesis but found that the LAI of grassland never increases above 2 5 m2m 2 Ecosystem phenology can also be track...

Page 15: ... efficiency term remains to be quantified in order to make accurate predictions of GPP Gamon et al 1990 1992 proposed a dual band vegetation index similar to the NDVI that could be used to estimate The founda tion of the measurement is based on the absorbance of xanthophyll pigments in a fairly narrow spectral region around 532 nm The xan thophyll cycle signal seen in reflectance at 532 nm has bee...

Page 16: ... of NDVI or PRI to contain high amounts of variability due to changing environmental and observa tion conditions Spectral reflectance measurements are inherently variable due to radiation source reflecting surface and sun sensor surface geometry Sometimes NDVI and or PRI values exhibit er ratic behavior due to changing environmental conditions Some level of data filtering e g visual inspection for...

Page 17: ...VI time series 1 Toward the beginning of the time series NDVI data increase until plateauing in early July when canopy closure occurred 2 There is a significant amount of high frequency variability mak ing it difficult to see this pattern clearly 3 One source of data variability is due to sun sensor surface ge ometry A concave diurnal pattern of NDVI is normal and is caused by the sun moving acros...

Page 18: ...e data were filtered and averaged by time but you can also use solar zenith and azimuth angles to filter you data For example Ryu et al 2012 sampled across a consistent solar elevation angle 60 each day ignoring all other values Using solar zenith an gle as a filter ensures that data from each day are collected under similar sun sensor surface illumination conditions 5 If you are comparing measure...

Page 19: ...ghly variable in space Reasonable distances between up looking and down looking sensors will depend on the typical radiation environment of a given location It is important to arrange paired up looking and down looking sen sors to collect data at the same time to account for temporal vari ability in radiation conditions In cases where multiple down looking sensors have been deployed within close p...

Page 20: ... a down facing sensor place a reflectance standard within the field of view of the field stop sensor making sure that the reflectance panel is uniformly illuminated and that the field of view of the sensor is fully within the area of the reflectance panel Mea surements obtained from field stop sensors pointed at the reflectance panel must be multiplied by π to convert radiance values to irradi anc...

Page 21: ... and the remote sensing of leaf canopy and ecosystem radiation use efficiencies A review and meta analysis Remote Sensing of the Environment 115 281 297 Garrity S R Vierling L A Bickford K 2010 A simple filtered photodiode instrument for continuous measurement of narrowband NDVI and PRI over vegetated canopies Agricultural Forest Me teorology 150 489 496 Garrity S R Eitel J U H Vierling L A 2011 D...

Page 22: ...a for Biomass Assessment of Small Grain Cereals Biomass Detection Production and Usage Darko Matovic Ed ISBN 978 953 307 492 4 InTech Available from http www intechopen com bo oks biomass detection production and usage field measurements of canopy spectra for biomass assessment of small grain cereals Ryu Y Baldocchi D D Verfaillie J Ma S Falk M Ruiz Mercado I Hehn T Sonnentag O 2012 Testing the pe...

Page 23: ...he top of the canopy The field stop and hemispherical versions can both be used to quan tify canopy reflected radiation The correct choice of sensor will depend on the objectives of the study The hemispherical sensor has a ground instantaneous field of view GIFOV of 180 full an gle and will do a better job of averaging reflected radiation over a broad area When using hemispherical view sensors in ...

Page 24: ...sensor above the canopy Consider a sen sor mounted 2 m above a canopy The GIFOV would be 2 tan 18 2 which equals a 1 3 m diameter circle If the field stop sensor is pointed off nadir no longer facing straight down then the GIFOV becomes elliptical When using the SRS in an off nadir view angle be sure that the field of view does not go above the horizon For help in calculating the FOV you can use t...

Page 25: ...rts on the data logger and use either our Utility application or other METER software software to configure that port for the SRS and set the measurement interval See data logger manual and quick start guide for more instructions METER data loggers have a threshold logging frequency When you set the logging interval to greater than this threshold on any METER logger reported readings are automatic...

Page 26: ...ctly to ME TER s data loggers Figure 8 shows the wiring configuration for this connector Figure 8 3 5 mm Stereo Plug Wiring 5 3 Connecting to a Non METER Logger Customers may purchase the SRS for use with non METER data loggers These sensors typically come configured with stripped and tinned pigtail wires for use with SDI BUS terminals Refer to your particular logger manual for details on wiring O...

Page 27: ...as Figure 10 shows Connect the supply wire brown to the excitation the digital out wire orange to a digital input and the bare ground wire to ground Figure 10 Pigtail End Wiring to Data Logger Note The acceptable range of excitation voltages is from 3 6 to 15 VDC If you wish to read the SRS with the Campbell Scientific Data Loggers you will need to power the sensors off of a 12 V or switched 12 V ...

Page 28: ...r it then cannot be easily used in the future with a METER readout unit or data logger Option 2 Obtain an adapter cable from METER The adapter cable has a connector for the stereo plug connector on one end and three wires or pigtail adapter for connection to a data logger The stripped and tinned adapter cable wires have the same termination as in Figure 10 the brown wire is excitation the orange i...

Page 29: ...must change Address options include 0 9 A Z a z There are two ways to set the SDI 12 sensor address The best and easiest is to use METER s ProCheck if the option is not available on your ProCheck please upgrade to the latest version of firmware Campbell Scientific data loggers like the CR10X CR1000 CR3000 among others also support SDI 12 Communication Direct SDI 12 communication is supported in th...

Page 30: ...6 COMMUNICATION SRS Sensors Reading the SRS in SDI 12 mode using a CSI datalogger requires a function call An example program from CRBasic can be found on our website at http www metergroup com 26 ...

Page 31: ...top sensors are mounted in a down looking orientation outputs include the calibrated spectral radiance W m 2 nm 1 sr 1 of each band and either NDVI or PRI If both up looking and down looking sensors of the same variety e g up looking hemispherical NDVI and down looking field stop NDVI are connected to the same data logger then α from the up looking sensor is combined with the spectral radiance val...

Page 32: ... intensities but if data from low radiation intensity periods are desirable manual calculation of the spectral reflectance index will result in best possible precision Note that these differences should not be present in EM60 ZL6 and future data logger offerings from METER Contact METER Support for more details support environment metergroup com 7 2 Using other data loggers When connected to non M...

Page 33: ... use hemispherical sensors in a down facing orientation but make sure to mount them facing directly down so they are not seeing sky The influence of the mounting infrastructure and sky can be avoided by using field stop radiometers Field stop sensors average over just the area within the field of view where you aimed them Assure that the area they see is representative and carefully choose the vie...

Page 34: ...e solution when cleaning the field stops since they can damage the op tical interference filters Outer surfaces of your SRS can be cleaned a soft damp cloth as necessary In the event that your SRS optics become extremely soiled it may be necessary to return to the factory for cleaning and re calibration See section 9 3 for more details on SRS calibration 30 ...

Page 35: ...you are using the cor rect versions of logger firmware and software 9 2 Sensors 1 Ensure that you install the sensors according to the Installa tion section of this manual 2 Check sensor cables for nicks or cuts that could cause a mal function 3 Check the sensor wavelength intensity results outside or under a bright light NDVI or PRI calculations may give no data or erroneous data at low intensiti...

Page 36: ... SRS Sensors rization RMA form to send your sensor in for recalibration Call or email METER at 509 332 5600 or support environment metergroup com to arrange for a RMA or to obtain your sensor calibration informa tion 32 ...

Page 37: ...man WA 99163 USA Type of Equipment Spectral Reflectance Sensor Model Number SRS Year of First Manufacture 2013 This is to certify that the SRS Spectral Reflectance Sensor manufac tured by METER Group Inc USA a corporation based in Pullman Washington USA meets or exceeds the standards for CE compliance as per the Council Directives noted above All instruments are built at the factory at METER and p...

Page 38: ... Support 1 Declaration of Conformity 33 Email 1 Field Installation 19 Fractional Interception 8 Installation 29 Leaf Area Index LAI 6 NDVI 6 Phenology 10 Photochemical Reflectance Index 1 Photosynthesis 10 Pigtail End Wiring 23 SDI 12 Communication 25 Seller s Liability 2 Specifications 4 Stereo Wiring 3 5 mm 22 Troubleshooting 31 Warranty 2 34 ...

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