916402 Description

1991 Camargue Sunflower Polarization (916402)

Revised (5-5-92)

The purpose of this experiment was to characterize the polarization of a sunflower field at various view and illumination angles in support of the POLDER aircraft missions. Data from two Barnes 12-1000 multiband radiometers were collected on June 24 (162 observations) and June 25 (110 observations). Reflectance polarization measurements were acquired in two Landsat Thematic Mapper wavelength bands (0.63-0.69 um, 0.76-0.90 um) plus a 1.15-1.30 um band at view zenith angles of 0, 10, 20, 30, 40, 50, 60 and 70 degrees and view azimuth angles of 0, 90, 180, 270 degrees relative to the solar illumination azimuth angle. Some polarization measurements were also made of the sky conditions for view zenith angles of 180 (straight up), 170, 160, 150 , 140, 130, 120, 110 degrees and view azimuth angles of 90, 180, and 270 degrees relative to the solar azimuth.

The radiometers were mounted on a platform built on the bucket of a boom truck. The boom truck was parked along the North to East edges of the sunflower field so that there would be no truck shadows within the field of view of the instruments. A set of data consisted of 2 azimuth angles - one in the plane of the sun (towards sun or towards hot spot) and one perpendicular to the plane of the sun (left or right of sun). No sky data were collected for the azimuth angle towards the sun so as not to risk damaging the detectors.

The field of view of the two multiband radiometers was 1 degree. The data were collected from a height of 6 meters above the canopy. There were three channels of data collected for each of the three wavelength bands listed above each having a polarizing film oriented at a different angle The three relative polarizer angles were 0, 45 and 90 degrees. Data were also collected for 5 wavelength bands with no polarizing film (0.45-0.52 um, 0.52-0.60 um, 2 of 1.55-1.75 um and 2.08-2.35 um).

Other measurements collected in conjunction with the reflectance measurements included leaf reflectance and transmittance, biomass, leaf area index, development stage and optical depth.

Descriptions of Some of the Units Used in the Data Files.

1. 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.

2. Irradiance Zenith Angle

This angle represents the direction of the solar disc measured from a vertical line passing through the earth at the sunflower field.

3. View Azimuth Angle

This angle represents the direction that the Barnes multiband radiometer is viewing towards measured clockwise from North.

4. 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.

5. Experimenter Parameter 1 (from Parameter Description File)

Raw data for the Barnes detector temperature.

6. Experimenter Parameter 2 (from Parameter Description File)

View azimuth angle with respect to the solar azimuth angle - 0 degrees towards the sun, 270 degrees is to the left of sun,- 180 degrees is towards the hot spot, 90 degrees is right of sun.

A summary of the data sets follow.
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Set  Time Range  Illumination Angles     View Azimuth Angles     Cloud  Scene
                  zenith    azimuth   relative to solar azimuth  Cover
       (GMT)          (degrees)               (degrees)           (%)
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6/24/91

1   10:32-10:35    25-25    138-140         0, 270                50   Sunflowers
2   11:13-11:17    21-21    160-163         0, 270                50   Sunflowers
3   11:58-12:01    20-21    189-191       180, 270                50   Sunflowers
4   12:04-12:07    21-21    194-195        90, 180, 270           50   Sky
5   13:11-13:16    27-28    229-230         0,  90                50   Sunflowers
6   13:41-13:46    32-32    239-241        90, 180, 270           60   Sky
7   14:15-14:19    37-38    249-250         0, 270                60   Sunflowers

6/25/91

1   10:56-11:01    23-22    150-153         0,  90, 180           10   Sunflowers
2   11:24-11:27    21-21    167-169        90, 180, 270           10   Sky
3   12:07-12:10    21-21    195-197         0,  90                10   Sunflowers
2   12:19-12:23    22-22    202-205        90, 180, 270           10   Sky

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