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Field Calibration/Validation Data » Field Data Collection Protocols » Sunphotometer Protocol - MicroTops Instrument

Sunphotometer Protocol - MicroTops Instrument

Last modified by Bec Trevithick on 2012/02/09 04:19

Site Details

 

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. [CU2If 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. Curtin Uni is trying to come up with a way of mounting the microtops to a portable, field deployable solar tracker.

[CU3]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 manual. 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 readngs 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. 

 
[CU4]I haven’t read the manual but as this is a hand held instrument and manually operated presumably readings are taken at the whim of the operator.  We should establish a sample rate to capture any variability. The Tumbarumba data exhibits a fair bit of variability in the AOT and an upward trend in water vapour and changes in the capture rate.  Increasing the sampling rate may make the data more noisy but it can always be average later.

[CU5]This may be alleviated by running the instrument all day. This would be far easier with a solar tracking system if we can work out how to do it cheaply and with fast setup. Otherwise some poor bugger has to stand around all day. If a solar tracking system were in place, the instrument could be run for the entire length of the field work. Need to aim the instrument at the sun if no sun tracker available. 10 channel awesomeness factor.

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

Recording of data in field

A log sheet for MicroTops measurements can be found LINK. This should be completed with each set of sunphotometer measurements.

 

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). 

 


 

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Created by Bec Trevithick on 2011/12/06 11:28

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