MicroTops Sunphotometer Protocol

Microtops instrument at Chowilla Supersite.

Site selection process

Select a site or sites preferably at the centre of the overall site of interest. This is in order to characterise atmospheric conditions most closely related to the image data being obtained. The site selected must be open and free from any potential obstructions between the observer and the solar disk. If this is not possible then place it where the targets will be. I would also collect data all day when the airborne capture is happening and ideally for the entire campaign.

It may be important to deploy in different location where site topography could cause big changes in water vapour or there was some localised production of aerosol (well travelled dirt road etc)

Description of plot layout

Record the single geographic point at which the measurements are made with GPS. Record the coordinates for any new sites moved to in the process of acquiring the measurements.

Basic data required

The following is essential data required for data management purposes:

Geographic coordinates (easting, northing, zone) recorded with a GPS (may be connected to the MicroTops instrument).
Operators: name those who collected the data and their affiliations
Date: consistent format (dd/mm/yyyy)
Time: Record the time measurements were begun from and when they ended.
Summary of general overhead sky conditions during the survey (particularly th presence of cloud, jet trails and haze).
Digital photographs of the major quandrants of sky or hemispheric photographs to characterise general overhead conditions (e.g. general degree of cloud cover).

Aside from a general data obtained above, essential data specific to each measurement is recorded directly by the MicroTops sunphotometer. If a GPS is connected, the sunphotometer can record the coordinates. Use of a separate GPS serves as a check on any positional errors that may arise.

Data collection process

Field equipment checklist

MicroTops sunphotometer
Microtops ozone meter (if available)
digital camera with hemispheric lens
tripods (1 specialised for mounting the microtops equipment).
Foldup Chair for sitting on.
microtops log sheet.

Process

Measurements are made using the MicroTops sunphotometer according to the method outlined in the MicroTops User Guide:

As an alternative summarised guides to the use of the instrument, with and without GPS attached are available from the NERC Field Spectroscopy Facility here.

For best results, the microtops instruments should be mounted on a tripod, or the operator should be seated and resting their elbows on their body such that the instrument is held as steady as possible on the solar disk during scans.

Make sure the GPS readings have stabilised before commencing recording with the MicroTops instrument. The initial measurements recorded may have erroneous GPS measurements and will need to be excluded from the record. Start the record from the point the GPS measurements stabilise.

Align the top of the camera to north.

Record a measurement with the microtops every 10 mins. At the same time, take a hemispheric photograph. Try to avoid being in the image, by ducking below the camera.

Data Recording and Storage

Electronic storage of data

Data will be recorded internally within the MicroTops sunphotometer. Guides to the downloading of the data are available from the NERC Field Spectroscopy Facility at: http://fsf.nerc.ac.uk/resources/guides/

Output will be stored as a csv file. This corrected data will be uploaded into the auscover spatial database (PostGIS) located on the UQ server, in two tables: sunphotometer (holding specific measurements for each observation) and field_obs (storing a geometry for the specific observation).