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. This experiment is a continuation of the sorghum polarization experiment begun in 1983. 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, 7, 15, 22, 30, 45, 60 and 70 or 75 degrees and view azimuth angles of 0, 45, 90, 135, 180, 225, 270, and 315 degrees. If the view azimuth angle was diagonal to the field boundaries, the maximum view zenith angle was 75 degrees. If the view azimuth angle was perpendicular to the field boundaries, the maximum view zenith angle was 70 degrees. One data set consists of two replications of 60 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 four days representing before and after heading development stages. 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. For the August dates, 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. For the September 19th date, the three 2.08-2.25 µm bands were replaced with three 1.55-1.75 µm bands.
Barnes-108 contained three 0.63-0.69 µm wavelength filters with polarizer film oriented at three different angles and three 1.15-1.30 µm wavelength filters with polarizer film oriented at three different angles. In addition, data were collected with a 0.52-0.60 µm wavelength band with no polarizer film.
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 for the first day, 8-17-84, was done under overcast conditions.
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.
7. Experimenter Parameter 9
Raw data for the Barnes detector temperature.
The summary of the data sets is in data_sets_summary_846401.txt file.
The test took place in 1984.
The supporting docs include a brief summary of used instruments, a wavelength table (Wavelength_ASCII.txt), reflectance note and reflectance tables (ReflectanceTable206.txt and ReflectanceTableMulti.txt), and file format description (ExperimentDataFormat3.txt). The format description file is in ASCII format in lines of 80 characters.
This research dataset is part the Field Research Data Library that consists of over 200,000 spectral observations of soils and vegetation that have been collected since 1972 till 1991 as part of the research focused on vegetation and soils at the Laboratory for Applications of Remote Sensing (LARS) located at the Purdue University.
Cite this work
Researchers should cite this work as follows:
- Vern C. Vanderbilt (2015). Purdue Agronomy Farm Sorghum Polarization (846401). Purdue University Research Repository. doi:10.4231/R7PC309T
- Location: Purdue Agronomy Farm, West Lafayette, IN
- County: Tippecanoe
- Latitude/Longitude: 0402813N 0865927W
- Illumination: Solar
- Experiment Type: Crops - Sorghum
- Spectral Instruments (Wavelength Range):
- Barnes 12-1000-105 (0.45-1.75 um): 846401.131.txt (5012 KB)
- Barnes 12-1000-108 (0.45-1.75 um): 846401.161.txt (5878 KB)