ISFF Deployment for SGS 2000
This page contains information being used to plan this field experiment,
which is scheduled for Sept. 2000. Expect it to change signficantly during
the year 2000.
Here is a partial list of phone numbers
and some driving directions.
Here is a "contact sheet" of photographs
taken by NCAR folks during SGS. Also, the Johns Hopkins folks have their
own set of photographs.
SGS requires that the wind and temperature fields be spatially filtered
in at least two dimensions -- along the wind and across the wind.
Using Taylor's hypothesis, filtering in the direction of the wind
can be accomplished by filtering in time.
However, to filter across the wind, multiple sensors placed
perpendicular to the wind direction are needed.
A digital filter can be made which reasonably approximates
a Gaussian filter using a minimum of 5 sensors.
Since SGS needs to apply a double filter to calculate second moments,
an overlapping array of five 5-sensor filters is needed at the same
This can be achieved with a line of 9 sonic anemometers, which also
is suitable for measuring lateral gradients (or differences) of
SGS also would like to measure the vertical difference between the filtered
fields. This requires an additional set of 5 sensors at a different height.
The core measurements for SGS will be from an
array of 14 sonic anemometers.
These 14 will consist of one set of 9 anemometers at one height and a second
set of 5 anemometers at another height. Both arrays will be equally spaced
in a line set up perpendicular to the wind. To minimize the number of
towers -- especially if individual tower are used -- the spacing at one
height should be double the spacing at the other height. It is desirable
to keep the ratio of spacing to height the same at both heights, so one
height must be double the first.
Vertical arrays of temperature, wind, and flux sensors will be placed on
three additional nearby towers to determine the mean turbulent structure
of the surface flux layer.
In order for the tower data to be used as a filter in the cross-wind
direction, the towers must be aligned as close as possible (on the
order of 10 degrees) perpendicular to the wind. Since we do not want
to move the towers frequently (very labor intensive), we need the wind
to come from a consistent wind direction. Wind climatology in the San
Joaquin Valley shows that winds are from 330 degrees (close to NW)
much of the time (both day and night) in most regions.
Since SGS will follow EBEX, we will know what the mean wind direction was
for the exact SGS site for the previous month.
The SGS measurement height requirements are height above the
effective zero-plane of the flow field.
Thus it is preferred to make the measurements in a fallow field to avoid
the additional zero-plane displacement height due to a crop canopy.
We would also like to have a uniform surface that extends in the upwind
(to the north-northwest) direction as far as possible, but hopefully for
a minimum of 1 mile.
To reduce the amount of effort, we hope to operate SGS from the same base
trailer as EBEX. However, this will require a fortuitous combination of
several sections of cotton adjacent to several sections of fallow, wheat,
or other crops to be harvested by September. (An ideal
layout is shown here.) If necessary, we will move
the base trailer as well, though we still would prefer to work with only
We have three potential sites for SGS. These are listed in my
site report. Housing will be at the
field experiment will end data collection on August 24,
allowing the transition of equipment to SGS to begin on August 25.
It is anticipated that SGS data collection may begin by September 3
or (hopefully) earlier.