TERRA-REF Documentation
WebsiteGitHubTutorials
revisions
revisions
  • Introduction
  • Data Sources
  • Software
  • Scientific Objectives and Experimental Design
    • Protocols
      • Controlled Environment Protocols
      • Manual Field Data Protocols
      • Phenotractor Protocols
      • Sensor Calibration
      • Template Protocol
      • UAV Protocols
    • Experimental Design
      • Experimental Design Danforth
        • Sorghum Lines Danforth
      • Experimental Design Genomics
        • Sorghum Lines Genomics Year 1
        • Sorghum Lines Genomics Year 1 (continued)
        • Sorghum Lines Genomics Year 2
      • Experimental Design MAC
  • User Manual
    • What Data is Available
    • Data Products
      • Environmental conditions
      • Fluorescence intensity imaging
      • Genomics data
      • Geospatial information
      • Hyperspectral imaging data
      • Infrared heat imaging data
      • Multispectral imaging data
      • Meteorological data
      • Phenotype data
      • Point Cloud Data
    • How to Access Data
      • Using Clowder (Sensor and Genoomics data)
      • Using Globus (Sensor and Genomics data)
      • Using BETYdb (trait data, experimental metadata)
        • Accessing BETYdb via ArcMap and other GIS software
      • Using CoGe (Genomics)
      • Using CyVerse (Genomics)
      • Using Analysis Workbench (all data)
    • Data Use Policy
    • Manuscripts and Authorship Guidelines
    • Release / reprocessing schedule
  • Technical Documentation
    • Data Standards
      • Existing Data Standards
      • Agronomic and Phenotype Data Standards
      • Genomic Data Standards
      • Sensor Data Standards
      • Data Standards Committee
    • Directory Structure
    • Data Storage
    • Data Transfer
    • Data Processing Pipeline
      • Geospatial Time Series Structure
    • Data Backup
    • Data Collection
    • Data Product Creation
      • Genomic Data
      • Hyperspectral Data
    • Quality Assurance and Quality Control
    • Systems Configuration
  • Developer Manual
    • Submitting data to Clowder
    • Submitting data to BETYdb
    • Submitting Data to CoGe
    • Developing Clowder Extractors
  • Tutorials
  • Appendix
    • Code of Conduct
    • Collaboration Tools
    • Glossary
Powered by GitBook
On this page
  • LemnaTec Field Scanalyzer
  • Calibration protocols
  • Calibration targets
  • Sensor Calibration
  • UAV calibration
  • Halogen spectrum
  • Spectral response data
Export as PDF
  1. Scientific Objectives and Experimental Design
  2. Protocols

Sensor Calibration

PreviousPhenotractor ProtocolsNextTemplate Protocol

Last updated 7 years ago

This section describes sensor calibration processes and how to access additional information about specific calibration protocols, calibration targets, and associated reference data.

LemnaTec Field Scanalyzer

Calibration protocols

Calibration protocols have been defined by LemnaTec in cooperation with vendors and the TERRA-REF Sensor Steering Committee. Draft calibration protocols are currently in and have been incorporated into the .

A detailed calibration process is also provided for the , with further information below.

Calibration targets

The following calibration targets are available:

  • Aluminum 3D test object

Sensor Calibration

Environmental sensor calibration

The environmental sensor has been calibrated by LemnaTec. The output of the spectrometer is raw counts, users will need to use the calibration files to convert to units of µW m-2 s-1, taking into account the bandwidth of the chip (0.4nm) if converting to µmol m-2 s-1.

Calibration reference data is available via Globus /sites/ua-mac/EnvironmentLogger/CalibrationDataor in Github

Hyperspectral calibration

Sources:

For the SWIR and VNIR sensors, factory calibration is repeated each year using the calibration lamp provided by Headwall. To convert the hyperspectral exposure image to reflectance requires the wavelength-dependent, factory calibrated reflectance of the spectralon at all VNIR and SWIR wavelengths and a good image of a spectralon panel from each camera. This includes periodic measurements of a white spectralon reflectance panel run with 20ms exposure to match panel calibration.

Dark reference measurement:

  • VNIR

    • Dark measurement for VNIR camera is taken at exposure times 20, 25, 30, 35, 40, 45, 50, 55ms.

    • Data is in the same hypercube format with 180-200 lines, 955 bands, and 1600 pixel samples.

    • Measurement was done using Headwall software, so there is no LemnaTec json file.

    • The name of the folder is the exposure time. "current setting exposure" is showing the exposure time in ms.

    • Custom workflow to process the calibration files.

  • SWIR;

    • Dark counts handled internally, so no calibration files are necessary.

White reference measurement:

  • VNIR

    • White measurement for VNIR camera is taken at exposure times 20, 25, 30, 25, 40, 25, 50, 55 ms.

    • The name of the folder is the exposure time. Data are 1600 sample, 955 bands and 268-298 lines. White reference is located in the lines between 60 to 100 and in the samples between 600 to 1000.

    • The white reference scans was done at around 1pm ( one hour after solar noon). I don’t see the saturation with 20ms and 25ms exposure time.

    • For the calibration, this needs to be subtracted from the dark current in the same sample, band and exposure time.

    • In the following file, I stored an extra file named "CorrectedWhite_raw". This file includes only a single white pixel( one line, one sample) in 955 bands for each exposure time. Data is stored in the similar format but it doesnot include any extra files like frameIndex, image, header ,..

      https:\/\/drive.google.com\/file\/d\/0ByXIACImwxA7dVNHa3pTYkFjdWc\/view?usp=sharing

      Let me know if you have issue with opening the files.

Stereo 3D height scanner

LemnaTec applied calibration matrix to the 3D scanners.

UAV calibration

  • There are calibrated reference panels and blackbody images taken with UAV sensors before and\/or after the each flight mission.

  • There are also 4 white,grey and black panels laid on the ground during the flight. Knowing the proprieties of these targets would helps us radiometrically correct the UAV images.

  • What are the reflectance properties of calibrated reference panels for multispectral camera?

  • What are the thermal properties of reference target for thermal camera?

  • What are the reflectance properties of the reference panels laid on the ground during the flight?

  • Is there any other ground truth data collected during the flight for aerial data processing, such as surface reflectance, temperature and other environmental data? These type of data would be helpful for further atmospheric correction.

  • There are two sets of reference reflectance panels: one that PDS uses, it is small, PDS will need to provide the specs; the second set consists of 4 8m x 8m canvas tarps, nominally 4%, 8%, 48% and 64% reflectance across vnir bands.

  • We have data from an ASD spectrometer on many but not all flight days that can be used to give the most accurate actual reflectances for each. Kelly Thorp can provide the numbers. The tarps are old and the dark targets are more reflective than nominal and light targets darker than nominal.

  • The thermal target is a passive black body, I dont know the surface emissivity, it is around 0.97. There are thermistors in the back of the metal plate to provide physical temperature of the body. The black body is stored in a wood box, insulated, to dampen thermal variations. Id guess it is accurate to 2C.

  • There is a met station on farm for air temperature, humidity, wind speed, wind direction, solar radiation. we have a sun photometer that can be used for atmospheric water vapor content but currently dont deploy it routinely.

Halogen spectrum

Spectral response data

Relative spectral response data is available for the following sensors:

  • NDVI

  • PRI

  • PAR

Calibration data

Data is available on Globus in /gantry_data/VNIR-DarkRef/ or via

Data is available via

Source:

No per-wavelength analysis of light produced by the halogen lights is available from the vendor for Showtec 240V\/75W. Measurements are available for a similar halogen bulb Philips Twistline Halogen 230V 50W 18072 in Github:

Where available, per device calibration certificates are included in the collections.

Google Drive
LemnaTec Scanalyzer Field sensor documentation
Hyperspectral sensors
LabSphere Spectralon Diffuse Color Targets
SphereOptics Zenith Polymer diffuse reflectance standards
Calibrations.zip
Convert hyperspectral exposure image to reflectance
Hyperspectral calibration protocols
Google Drive.
Google Drive.
https://github.com/terraref/computing-pipeline/issues/185
MeasurementPhilipsHalogenSpot.xlsx.
Device and Sensor information