Please use this identifier to cite or link to this item: https://hdl.handle.net/1959.11/14215
Title: A Comparison of Two Ranging Approaches in an Active, Optical Plant Canopy Sensor
Contributor(s): Schaefer, Michael T  (author); Lamb, David  (author); Bradbury, Ronald  (author)
Publication Date: 2014
Handle Link: https://hdl.handle.net/1959.11/14215
Abstract: Active optical sensors that contain their own modulated light sources are becoming popular for 'sensing' photosynthetically-active biomass in crops and pastures. These sensors detect optical reflectance to derive spectral vegetation indices, such as the normalised difference vegetation index (NDVI), and are subsequently calibrated to measure plant parameters e.g. biomass. However, research has demonstrated the accuracy of the derived measurements can often be improved by including both a spectral index and a corresponding measure of plant height. This paper describes an active, optical sensor that integrates modulated reflectance sensing with the ability to measure (range) the distance between the source and a target surface. Two ranging techniques are evaluated; one based on the inverse square law (ISL) of reflected radiation and another based on a position-sensitive detector (PSD). Both ranging methods proved capable of reliably delineating target distances out to 4.0 m from the source. Over this range, the PSD detector exhibited a distance-invariant RMSE of ± 2.6 cm whilst the ISL method exhibited an almost linear increase in error of ± 25 % of the measured distance to a spectralon target. Application to a vegetative target (Kikuyu grass), demonstrated the ISL ranging method to yield an average RMSE of ± 3.0 cm in the range of 0.60-1.40 m, while the average RMSE of the PSD over a range of 0.50-1.10 m was observed to be ± 10.0 cm. Despite superior accuracy, target reflectance variations may prove problematic in the use of a PSD ranging sensor and requires further investigation.
Publication Type: Conference Publication
Conference Name: SAS 2014: IEEE Sensors Applications Symposium, Queenstown, New Zealand, 18th - 20th February, 2014
Conference Details: SAS 2014: IEEE Sensors Applications Symposium, Queenstown, New Zealand, 18th - 20th February, 2014
Source of Publication: IEEE Sensors Applications Symposium Proceedings, p. 253-257
Publisher: IEEE: Institute of Electrical and Electronics Engineers
Place of Publication: Piscataway, United States of America
Field of Research (FOR): 020501 Classical and Physical Optics
070104 Agricultural Spatial Analysis and Modelling
Socio-Economic Outcome Codes: 830406 Sown Pastures (excl. Lucerne)
Peer Reviewed: Yes
HERDC Category Description: E1 Refereed Scholarly Conference Publication
Other Links: http://sensorapps.org/sites/default/files/uploads/SAS-2014_web_program_feb-17.pdf
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