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Lars Eklundh

Professor

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

Författare

  • Hongxiao Jin
  • Lars Eklundh

Summary, in 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.

Avdelning/ar

  • Institutionen för naturgeografi och ekosystemvetenskap
  • MERGE: ModElling the Regional and Global Earth system
  • BECC: Biodiversity and Ecosystem services in a Changing Climate

Publiceringsår

2015

Språk

Engelska

Sidor

3405-3416

Publikation/Tidskrift/Serie

IEEE Transactions on Geoscience and Remote Sensing

Volym

53

Issue

6

Dokumenttyp

Artikel i tidskrift

Förlag

IEEE - Institute of Electrical and Electronics Engineers Inc.

Ämne

  • Physical Geography

Nyckelord

  • 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

Status

Published

Projekt

  • NordSpec - a research network for spectral data collection

ISBN/ISSN/Övrigt

  • ISSN: 0196-2892