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In Situ Calibration of Light Sensors for Long-Term Monitoring of Vegetation

Author:
  • Hongxiao Jin
  • Lars Eklundh
Publishing year: 2015
Language: English
Pages: 3405-3416
Publication/Series: IEEE Transactions on Geoscience and Remote Sensing
Volume: 53
Issue: 6
Document type: Journal article
Publisher: IEEE - Institute of Electrical and Electronics Engineers Inc.

Abstract english

Light sensors are increasingly used to monitor vegetation growing status by measuring reflectance or transmittance in multispectral or photosynthetically active radiation (PAR) bands. The measurements are then used to estimate vegetation indices or the fraction of absorbed PAR (FPAR) in a continuous and long-term manner and to serve as inputs to environmental monitoring and calibration/validation data for satellite remote sensing. However, light-sensor calibration is often overlooked or not properly attended to, which leads to difficulties when comparing the measurement results across sites and through time. In this paper, we investigate a practical and accurate user-level in situ calibration method in daylight. The calibration of a sensor pair is made for measuring either bihemispherical reflectance or hemispherical-conical reflectance, which are the two most common ground-based spectral measurements. Procedures and considerations are suggested for user calibration. We also provide a method for calibrating and measuring a single-sensor reflectance-derived Normalized Difference Vegetation Index (NDVI) from red and near-infrared bands. The calibration error propagation is analyzed, and the induced uncertainties in vegetation reflectance and in the NDVI are evaluated. The analysis and field measurements show that the NDVI estimated from a user calibration factor can be as accurate as, or even more accurate than, the manufacturer's calibration. The in situ calibration described here remedies the situation where reflectance for large field-of-view sensors cannot be always estimated from the manufacturer's calibration. The method developed in this paper may help improve the reliability of long-term field spectral measurements and contributes to the near-surface remote sensing of vegetation.

Keywords

  • Physical Geography
  • Calibration
  • error propagation
  • fraction of absorbed photosynthetically
  • active radiation (FPAR)
  • light sensor
  • near-surface remote sensing
  • Normalized Difference Vegetation Index (NDVI)
  • reflectance
  • uncertainty
  • vegetation monitoring

Other

Published
  • NordSpec - a research network for spectral data collection
  • ISSN: 0196-2892
E-mail: lars [dot] eklundh [at] nateko [dot] lu [dot] se

Professor

Dept of Physical Geography and Ecosystem Science

+46 46 222 96 55

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Dept of Physical Geography and Ecosystem Science

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Department of Physical Geography and Ecosystem Science
Lund University
Sölvegatan 12
S-223 62 Lund
Sweden

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