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

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SRS
Spectral Reflectance Sensor
Operator's Manual
METER Group, Inc. USA
14597-02

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Summary of Contents for METER Group, Inc. Spectral Reflectance Sensor

  • Page 1 Spectral Reflectance Sensor Operator’s Manual METER Group, Inc. USA 14597-02...
  • Page 2 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 Email: support.environment@metergroup.com or sales.environment@metergroup.com METER Group, Inc. USA c 2006-2019 All Rights Reserved...

  • Page 3: Table Of Contents

    SRS Sensors CONTENTS Contents 1 Introduction 1.1 Customer Support ....1.2 About This Manual ....1.3 Warranty .
  • Page 4 CONTENTS SRS Sensors 8 Installing the SRS 8.1 Attaching and Leveling ....29 8.2 Cleaning and Maintenance ....29 9 Troubleshooting 9.1 Data Logger .

  • Page 5: Introduction

    SRS Sensors 1 INTRODUCTION 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.

  • Page 6: About This Manual

    1 INTRODUCTION SRS Sensors About This Manual Please read these instructions before operating your sensor to ensure that it performs to its full potential. 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.

  • Page 7: About Srs

    SRS Sensors 2 ABOUT SRS About SRS 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.

  • Page 8: Specifications

    2 ABOUT SRS SRS Sensors Figure 2: Field Stop Version Figure 1: Hemispherical Version 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...
  • Page 9 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...

  • Page 10: Theory

    3 THEORY SRS Sensors 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.
  • Page 11 SRS Sensors 3 THEORY diometer. See Royo and Dolors (2011) for an extensive introduction to using spectral indices for plant canopy measurements. Figure 3: Reflectance spectra for bare soil (Soil) and a healthy wheat crop at various stages of development: heading (H), anthesis (A), milk-grain stage (M), and post maturity (PM).

  • Page 12: Estimating Lai

    3 THEORY SRS Sensors Estimating LAI NDVI has been shown to correlate well with green LAI, although the relationship is crop- or canopy-specific. For example, Aparicio et al. (2002) studied NDVI versus LAI in more than twenty different durum wheat genotypes in seven experiments over two years and found the relationship shown in Figure 4.
  • Page 13 SRS Sensors 3 THEORY phy and ceptometer techniques), the measurement of NDVI becomes less and less sensitive as LAI increases above a certain point (Figure 4). Nguy-Robinson et al. (2012) suggest changes in LAI are difficult to detect when LAI is much greater than 3 m .

  • Page 14: Canopy Phenology

    3 THEORY SRS Sensors Figure 5: Relationship between fractional canopy interception and NDVI, where NDVI is converted to LAI using Nguy-Robinson et al. (2012). Campbell and Norman (1998) give the relationship between LAI and fractional interception. Canopy Phenology Like all spectral measurements, NDVI is an indirect measurement. Over the years, researchers have correlated NDVI to several param- eters of interest, like LAI and f s, biomass, and canopy productiv- ity, among others.

  • Page 15: Photochemical Reflectance Index (Pri)

    SRS Sensors 3 THEORY Photochemical Reflectance Index (PRI) As described above, researchers use NDVI primarily as a proxy for canopy structural variables. Although structural properties are crit- ical, sometimes it is useful to have information about canopy func- tional properties. For example, estimating gross primary productiv- ity (GPP) of ecosystems is critical for modeling the global carbon balance.

  • Page 16: Sun-Sensor-Surface Geometry Considerations

    3 THEORY SRS Sensors quantum yield, maximum photosynthesis rate, electron transport un- der saturating light, non-photochemical quenching, and chlorophyll to carotenoid content ratio (Sims & Gamon, 2002; Garrity et al., 2011; Garbulsky et al., 2011; Porcar-Castell et al., 2012). Garbul- sky et al.
  • Page 17 SRS Sensors 3 THEORY Figure 6: NDVI data collected at five minute intervals from a corn canopy. B) Daily mean NDVI (blue circles) and smoothed daily NDVI (red line), substantially reduce the high frequency variability in the original NDVI time series. 1.
  • Page 18 3 THEORY SRS Sensors Figure 7: A subset of the data displayed in Figure 6, showing a single day of NDVI data. Notice the concave pattern that is typical in diurnal NDVI measurements. The concave pattern is due to changing sun-sensor-surface illumination geometry throughout the day.

  • Page 19: Calculating Percent Reflectance From Paired Up And Down Looking Sensors

    SRS Sensors 3 THEORY eters, can be used to reduce variations that arise from changes in sun-sensor-surface geometry across diurnal time scales. For additional details on BRDF normalization of vegetation index time series, see Hilker et al. (2008). Calculating Percent Reflectance from Paired Up and Down Looking Sensors Equation 1 shows that NDVI is the ratio of the difference to the sum of NIR and red reflectances.
  • Page 20 3 THEORY SRS Sensors Where α = I , equation 4 allows the computation of NDVI from just the down facing measurements if you know the ratio of red to NIR spectral irradiance, α. Although not extensively tested, we have found that this ratio (α...
  • Page 21 SRS Sensors 3 THEORY chlorophyll fluorescence in sunflower leaves and canopies. Oecologia, 85: 1-7. Gamon, J.A., Peuelas, J., Field, C.B., (1992). A narrow-waveband spectral index that tracks diurnal changes in photosynthetic effi- ciency. Remote Sensing of Environment, 41: 35-44. Gamon, J. A., Serrano, L., Surfus, J. S., (1997). The photochemical reflectance index: an optical indicator of photosynthetic radiation use efficiency across species, functional types, and nutrient levels.
  • Page 22 3 THEORY SRS Sensors 281: 277-294. Nguy-Robertson, A. Gitelson, A., Peng, Y., Via, A., Arkebauer, T., and Rundquist, D., (2012). Green leaf area index estimation in maize and soybean: Combining vegetation indices to achieve maximal sen- sitivity. Agronomy Journal, 104: 1336-1347. Porcar-Castell, A., Garcia-Plazaola, J.

  • Page 23: Field Installation

    SRS Sensors 4 FIELD INSTALLATION 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.
  • Page 24 4 FIELD INSTALLATION SRS Sensors rather than the vegetation in the inter-spaces. The GIFOV of a field stop SRS that is mounted in the nadir position (i.e., looking straight down) is determined by two factors: the angular field of view (which is fixed at 18 (half angle)) and the height of the sensor above the canopy.

  • Page 25: Connecting The Srs

    SRS Sensors 5 CONNECTING THE SRS Connecting the SRS Connecting to METER Data Logger The SRS is most easily used with METER’s data loggers. SRS sen- sors can also be used with other SDI-12 enabled data loggers, such as those from Campbell Scientific, Inc. The SRS requires an excitation voltage in the range of 3.6 to 15 volts.

  • Page 26: 3.5 Mm Stereo Plug Wiring

    5 CONNECTING THE SRS SRS Sensors If customers require logging intervals shorter than our logging thresh- old, then they must use a Campbell Scientific or similar logger capa- ble of recording data at the desired frequency. 3.5 mm Stereo Plug Wiring The SRS for METER loggers ships with a 3.5 mm stereo plug con- nector.

  • Page 27: Pigtail End Wiring

    SRS Sensors 5 CONNECTING THE SRS Pigtail End Wiring Figure 9: Pigtail End Wiring Note: Some SRS sensors may have the older Decagon wiring scheme where the power supply is white, the digital out is red, and the bare wire is ground. Connect the wires to the data logger as Figure 10 shows.
  • Page 28 5 CONNECTING THE SRS SRS Sensors wish to connect it to a non-METER data logger, use one of the fol- lowing two options. Option 1 1. Clip off the stereo plug connector on the sensor cable 2. Strip and tin the wires. 3.

  • Page 29: Communication

    SRS Sensors 6 COMMUNICATION Communication The SRS communicates using SDI-12 and DDI Serial protocols. This chapter discusses the specifics of SDI-1 Communication. For more information, please visit http://www.metergroup.com for an Integra- tor’s guide that gives more detailed explanations and instructions. SDI-12 Communication The SRS communicates using the SDI-12 and DDI Serial protocols, a three-wire interface where all sensors are powered (brown wire),...
  • 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.

  • Page 31: Understanding Data Outputs

    SRS Sensors 7 UNDERSTANDING DATA OUTPUTS Understanding Data Outputs Using METER’s Data Loggers Each SRS sensor generates multiple outputs when connected to a METER data logger. The exact outputs will in part depend on how many and what type of SRS sensors are attached to the data logger.

  • Page 32: Using Other Data Loggers

    7 UNDERSTANDING DATA OUTPUTS SRS Sensors down looking sensors are connected to different data loggers, you can export tabular data as Excel files and manually combine α from the up looking sensor with the spectral radiance values from the down looking sensor to calculate NDVI or PRI.

  • Page 33: Installing The Srs

    SRS Sensors 8 INSTALLING THE SRS Installing the SRS Attaching and Leveling The SRS comes with a variety of mounting hardware, allowing it to be mounted on poles, tripods, towers, etc. The mounting hardware allows for vertical adjustment and orientation on the pole and allows for sensor tilt.
  • Page 34 8 INSTALLING THE SRS SRS Sensors cleaned with a soft, damp cloth. Field stops can be cleaned with compressed air or cotton swabs. Do not use any type of volatile solution when cleaning the field stops since they can damage the op- tical interference filters.

  • Page 35: Troubleshooting

    SRS Sensors 9 TROUBLESHOOTING Troubleshooting Any problem with the SRS will most likely manifest as failed com- munication or erroneous readings. Before contacting METER about the sensor, please check these troubleshooting steps. Data Logger 1. Check to make sure the connections to the data logger are both correct and secure.
  • Page 36 9 TROUBLESHOOTING 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.

  • Page 37: Declaration Of Conformity

    SRS Sensors 10 DECLARATION OF CONFORMITY Declaration of Conformity Application of Council Directive: 2004/108/EC and 2011/65/EU Standards to which conformity is EN61326-1:2013 declared: EN550581:2012 Manufacturer’s Name: METER Group, Inc. USA 2365 NE Hopkins Ct. Pullman, WA 99163 USA Type of Equipment: Spectral Reflectance Sensor Model Number: Year of First Manufacture:...
  • Page 38 Index Calibration, 31 CE Compliance, 33 Cleaning, 29 Connecting Sensors Non-METER Logger, 22 Connecting the Sensors, 21 Contact Information, 1 Customer 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,...

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