916401 Description

1991 La Crau Rock Field Polarization (916401)

Revised (5-5-92)

The purpose of this experiment was to characterize the polarization of the La Crau 'rock 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 August 6 (625 observations). Reflectance polarization measurements were acquired in three Landsat Thematic Mapper wavelength bands (0.52-0.60 um, 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, and 270 degrees relative to the solar illumination azimuth angle. 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. A set of data consisted of two to four azimuth angles - in the plane of the sun (towards sun and/or towards hot spot) and perpendicular to the plane of the sun (left and/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 ?? meters above the ground. Three channels of data were collected for each of the four 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 1 wavelength band with no polarizing film (2.08-2.35 um).

Other measurements collected in conjunction with the reflectance measurements include optical depth.

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

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 (serial number 105) detector temperature.

6. Experimenter Parameter 2 (from Parameter Description File)

Raw data for the Barnes (serial number 108) detector temperature.

7. Experimenter Parameter 3 (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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8/6/91

1   10:51-11:00    29-28    152-156         0,  90, 180, 270       0   Rock Field
2   11:33-11:45    27-27    173-180         0,  90, 180, 270       0   Rock Field
3   12:10-12:15    27-27    193-195         0,  90, 180, 270       0   Rock Field
4   12:19-12:22    28-28    197-199        90, 180, 270            0   Sky
5   12:46-12:50    30-30    210-212         0,  90, 180, 270       0   Rock Field
6   12:53-12:55    30-30    213-214        90, 180, 270            0   Sky
7   13:13-13:18    32-33    222-223         0,  90, 180, 270       0   Rock Field
8   13:21-13:23    33-34    224-225        90, 180, 270            0   Sky
9   14:07-14:11    40-41    239-240         0,  90, 180, 270       0   Rock Field
10  14:15-14:17    41-42    241-242        90, 180, 270            0   Sky
11  14:35-14:39    44-45    247-248         0,  90, 180, 270       0   Rock Field
12  14:47-14:49    47-47    250-250        90, 180, 270            0   Sky
13  15:05-15:10    50-51    254-255         0,  90, 180, 270       0   Rock Field
14  15:14-15:19    51-52    256-257         0,  90, 180, 270       0   Rock Field
15  15:24-15:27    53-53    258-258        90, 180, 270            0   Sky
16  15:46-15:54    57-58    262-263         0,  90, 180, 270       0   Rock Field
17  16:02-16:11    60-61    265-266         0,  90, 180, 270       0   Rock Field
18  16:14-16:18    62-63    267-268        90, 180, 270            0   Sky

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