Delta SS1-UM-1.05 User Manual download pdf (Page 82)

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• Appendices Document code: SS1-UM-1.05

F. Glossary

Beam fraction - the fraction of the Total incident PAR in the Direct beam.

Beam Fraction Sensor (BFS) - consists of two PAR sensors and a shade ring, used

for measuring Direct and Diffuse light above the canopy.

Beer’s law - a general law describing transmission through an absorbing medium.

The intensity falls off exponentially with distance through the medium.

Cosine response - the response of a sensor to a ray of light is proportional to the

cosine of the angle of incidence of the ray (measured from the perpendicular to the

sensor surface).

CSV (Comma Separated Variable) a file format intended for importing into

spreadsheet or database programs. Fields are separated by commas, text is enclosed

in quotes.

Data Collection Terminal - the Psion Workabout handheld computer, used for

driving the SunScan probe, and presenting and storing the results.

Diffuse light - light scattered in the atmosphere. It is treated as coming from all parts

of the sky with equal intensity i.e. a Uniform Overcast Sky.

Direct beam - light coming directly from the sun, with no scattering. Usually treated

as if it comes from a point source.

ELADP - see Leaf Angle Distribution

Emulator - a setting in the SunData software that generates random results,

regardless of whether a SunScan probe is connected. Useful for learning to use the

software.

GMT - Greenwich Mean Time, also called Universal Time (UT). The standard time

used for astronomical measurements and calculations.

Hemispherical response - the response of the sensor is equal for all light rays

coming from above the plane of the sensor surface, independent of angle.

LAD - see Leaf Angle Distribution.

LAI - see Leaf Area Index.

Leaf absorption - the fraction of intercepted PAR that is actually absorbed by the

leaf. The remainder is reflected or scattered.

Leaf Angle Distribution - a way of describing the distribution of orientations in

space of the canopy elements. We model this using the Ellipsoidal Leaf Angle

Distribution, which describes the distribution of canopy elements as in the same

proportions as the surface of an ellipsoid. Using this model, a wide range of different

canopy types can be described by a single parameter, the Ellipsoidal Leaf Angle

Distribution Parameter (ELADP), which is the ratio of the horizontal to vertical axes

of the ellipsoid. An ELADP much greater than 1 describes a canopy of mostly

horizontal leaves, an ELADP near 0 describes a canopy of mainly vertical leaves.

Leaf Area Index (LAI) - the surface area of leaf per unit of ground area (assuming

leaves are flat, and including only one side of each leaf). Instruments like the

SunScan cannot differentiate between leaf and stem, so could more correctly be said

to estimate Plant Area Index.

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Delta SS1-UM-1.05 User Manual Page 82

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