The purpose of this experiment is to characterize the polarization of a sorghum field at various view and illumination angles and by its physical and agronomic attributes. Reflectance measurements were acquired in the three Landsat Thematic Mapper wavelength bands plus a 1.15-1.30 µm band at view zenith angles of 0, 15, 30, 45, 60 and 65 degrees and view azimuth angles of 0, 45, 90, 135, 180, 225, 270, and 315 degrees. One data set consists of two replications of 44 view angles each. The radiometers were mounted on top of a tower in the middle of the sorghum field. The tower system is described by Jon Ranson in "Sun-View Angle Effects on Reflectance Factors of Corn Canopies", Remote Sensing of Environment, 18:147-161 (1985).
The field of view of the two Barnes 12-1000 multiband radiometers that were used was 15 degrees and the vertical height of the multiband radiometer was 5.9 meters above the ground. These data were collected for various solar zenith and azimuth angles during two days. An ancillary data set was collected in conjunction with reflectance measurements to describe the sorghum field by its canopy geometry, ground cover, biomass, leaf area index and development stage. Vern Vanderbilt has this information.
The data were collected with a pair of Barnes 12-1000 multiband radiometers that contained a modified set of wavelength filters and polarizers. Barnes-105 contained three 0.45-0.52 µm wavelength filters with polarizer film oriented at three different angles mounted on the front plate of the instrument. In other words the light would pass through the polarizer film first and then through the wavelength filters. Barnes-105 also contained three 2.08-2.35 µm wavelength filters. with polarizer film oriented at three different angles. In addition, data were collected with a 0.76-0.90 µm wavelength band with no polarizer film.
Barnes-108 contained three 0.63-0.69 µm wavelength filters with polarizer film oriented at three different angles, two 1.15-1.30 µm wavelength filters and one 1.55-1.75 µm wavelength filter with polarizer film oriented at three different angles (The 1.55-1.75 filter was supposed to have been a 1.15-1.30 filter; the error was not noticed until after the data had been collected.)
No data were collected with the Barnes thermal channels. The three relative polarizer angles were 0, 45 and 90 degrees. One can determine what the polarization is by using the measurements from the three polarizing angles.
The data collection for the first day, 9-27-83, was considered practice.
LARSPEC Identification Record Codes
1. Scene Type
The pair of numbers after 'SORGHUM' indicate the view zenith and azimuth directions - azimuth first, zenith last. The view zenith and azimuth angles are also stored in the LARSPEC identification records under view zenith angle (VIZE) and view azimuth angle (VIAZ), respectively.
2. Irradiance Azimuth Angle
This angle represents the direction of the solar disc measured clockwise from North. In other words it is the azimuthal angle from which the directional solar rays are coming.
3. Irradiance Zenith Angle
This angle represents the direction of the solar disc measured from a vertical line passing through the earth at the sorghum field.
4. View Azimuth Angle
This angle represents the direction that the Barnes multiband radiometer is viewing towards measured clockwise from North.
5. View Zenith Angle
This angle represents the direction that the Barnes multiband radiometer is viewing measured from a vertical line passing through the earth at the sorghum field.
6. Plot Numbers
201 refers to sorghum scene.observations.
203 refers to sky observations.
204 refers to shaded reflectance reference panel observations.
A summary of the data sets follows.
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Set Time range Illumination Angles Cloud Scene
zenith azimuth Cover
(GMT) (degrees) (%)
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9/27/83
1 17:45-18:00 42-42 182-187 ? Sorghum
2 18:08-18:17 42-43 190-194 ? Sky
3 19:28-19:41 48-50 217-221 ? Sorghum
4 19:48-19:53 51-52 223-224 65 Sorghum
5 20:06-20:15 54-55 228-230 65 Sky
9/28/83
1 14:49-15:03 57-55 126-130 0 Sorghum
2 15:10-15:17 54-53 132-134 0 Sky
3 15:41-15:53 50-49 140-143 0 Sorghum
4 16:29-16:39 45-44 155-158 0 Sorghum
5 16:45-16:50 44-44 160-162 1 Sky
6 16:58-17:11 43-43 165-170 3-5 Sorghum
7 17:56-18:06 42-43 186-190 5 Sorghum
8 18:14-18:21 43-43 193-195 5 Sky
9 19:11-19:28 47-49 212-217 0 Sorghum
10 19:37-19:45 50-51 220-222 0 Sky
11 20:11-20:25 55-57 229-232 0 Sorghum
12 20:34-20:40 58-59 234-236 0 Sky
13 21:07-21:19 63-65 242-244 0 Sorghum
14 21:28-21:35 67-68 246-247 0 Sky
15 22:09-22:13 74-75 254-254 0 Sorghum
16 22:20-22:26 76-77 255-257 0 Sky
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