Sunphotometer data was collected on 17th June 2006 using three identical Microtops II instruments, as part of the Network for Calibration and Validation of Earth Observation data (NCAVEO) 2006 field experiment. The instruments were operated at three locations near Chilbolton: the roof of Chilbolton Facility for Atmospheric and Radio Research's (CFARR) main building, the Hampshire Golf Club and Cowdown Farm.

On using the three instruments together on the roof of the CFARR main building, results showed differences between the three instruments, with data from s/n 8407 being closest to that measured by the Cimel sunphotometer at the same location. Note that the date of s/n 8407 was set incorrectly to 2005, but has been corrected in the NASA Ames formatted file. This should not affect the data collected. The same instrument also did not record the water vapour amount, so this is shown as -999.0 in the data file. On the ‘golden day’, 17th June 2006, measurements were made with all three instruments every five minutes between 09:30 and 11:30 GMT. Sporadic measurements were also made at earlier and later times. The s/n 8407 did not make a reading at 11.15 as anticipated. A large number of parameters and calibration constants were used to achieve these readings and are included alongside the main data. For further information please refer to the Microtops II User’s Guide.