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ARS Home » Plains Area » Sidney, Montana » Northern Plains Agricultural Research Laboratory » Agricultural Systems Research » Research » Publications at this Location » Publication #192602

Title: Bidirectional Effect on a Spectral Image Sensor for in-Field Crop Reflectance Assessment

Author
item Kim, James
item Reid, John

Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2007
Publication Date: 1/22/2007
Citation: Kim, Y., Reid, J.F. 2007. Bidirectional Effect on a Spectral Image Sensor for in-Field Crop Reflectance Assessment. International Journal of Remote Sensing. 28(21):4913-4926.

Interpretive Summary: In-field crop sensory measurements are made under natural ambient illumination and influenced by sunlight intensity that varies over time and affects spectral responses at all stages of plant growth. This paper reports the effect of bidirectional light reflection on an image-based reflectance sensor designed for plant N assessment. Experiment presented the non-linearity of reflectance responses generated by varying solar positions. Ambient illumination was analyzed and compensated for horizontally fixed postures of an ambient illumination sensor and spectral image sensor. A compensation algorithm was developed to correct for non-linearity of both sensors. The compensated reflectance was consistent against the varying solar zenith angle throughout the daytime within acceptable variation at all three green, red, and near-infrared spectral channels regardless of sunny and cloudy conditions.

Technical Abstract: In-field spectral measurements are made under natural ambient illumination and influenced by solar radiation that varies over time and affects spectral responses at all stages of plant growth. This paper reports the effect of bidirectional light reflection on an image-based reflectance sensor designed for plant N assessment. Experiment presented the non-linearity of reflectance responses generated as a function of solar zenith angle. Ambient illumination was analyzed and compensated for horizontally fixed postures of an ambient illumination sensor and spectral image sensor. A compensation algorithm was developed to correct for non-linearity of both sensors. The compensated reflectance was consistent against the varying solar zenith angle throughout the daytime within maximum standard deviation of 0.62% at all three green, red, and near-infrared spectral channels, when testing with a 20% reflectance panel.