The purpose of this experiment is to characterize a spring wheat canopy by its reflectance at various view and illumination angles and by its physical and agronomic attributes. Reflectance measurements were acquired from 0.46 to 2.40 um using an Exotech model 20C spectroradiometer. at view zenith angles of 0, 15, 30, 45 and 60 degrees and view azimuth angles of 0, 45, 90, 135, 180, 225, 270, and 315 degrees. Spectral data and a photograph of the instrument field of view were taken in each of the 33 view directions. The field of view of the Exotech 20C was 15 degrees and the vertical height of the system above the soil was 7.6 meters. These data were collected for various solar zenith and azimuth angles during five days each representing a different development stage for the spring wheat canopy. Measurements were also made of leaf transmittance. An ancillary data set was collected in conjunction with reflectance measurements to describe the spring wheat field by its canopy geometry, ground cover, biomass, leaf area index and development stage.
On two of the four days, June 19 and July 17, polarization measurements were collected. The polarization data for these days only include wavelengths from 0.46-0.72 um since the polarizing material that was used was only good for the visible wavelengths. A polarization analyzer, a sheet of polarizing film mounted in a rotateable bracket, was attached to the spectroradiometer at the entrance port. In each view direction, two spectra were acquired, one with the polarization analyzer oriented for maximum detector signal amplitude and the other with the analyzer oriented for minimum signal. See reference for details of an analysis of this polarization data.
A summary of the data sets follows.
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Set Time range Illumination Angles Cloud
zenith azimuth Cover
(GMT) (degrees) (%)
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6/19/76 (Polarization Data)
1 16:13-18:26 41-25 113-164 1
2 19:33-20:44 26-33 200-230 1-20
6/21/76
1 14:58-15:31 53-47 96-103 1
2 15:48-16:20 45-40 107-115 1
3 18:04-18:36 27-25 152-169 1
4 18:57-19:23 25-25 180-194 1
5 19:59-20:29 28-31 212-225 1
6 20:51-21:18 34-37 233-241 1
7 21:54-22:20 43-47 251-257 1
8 22:34-22:58 49-53 260-265 1
9 23:19-23:42 57-61 269-273 1
7/17/76 (Polarization Data for some sets)
1 15:35-16:03 49-45 105-111 2
2 16:17-16:46 42-38 115-123 2
3 17:03-18:20 36-28 128-159 2 (P)
4 19:04-19:36 27-28 182-198 2
5 20:04-20:34 30-33 211-223 2
6 20:56-22:00 35-45 231-249 2-4 (P)
7 22:30-23:07 49-55 256-264 6
8 23:18-23:50 57-63 266-272 6
9 00:13-00:34 67-70 276-280 6
7/31/76
1 15:27-15:52 52-48 105-111 5-30
2 16:06-16:34 46-42 115-122 5
3 17:00-17:29 39-35 130-140 5
4 17:46-18:14 34-31 146-158 5
5 18:57-19:30 30-30 178-194 10
6 20:02-20:34 32-35 208-220 10
7 21:05-21:33 39-43 231-239 10
8 21:42-22:15 44-49 242-250 10
9 22:30-23:04 52-57 253-261 10
10 23:19-23:55 60-66 264-270 10
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Vanderbilt, Vern, et al. "Specular, diffuse, and polarized light scattered by two wheat canopies", Applied Optics, Vol. 24, No. 15, August 1, 1985.