title: An infrared filter radiometer for atmospheric cluster-ion detection.
abstract: Motivated by the detection of infrared absorption bands from atmospheric cluster ions in laboratory experiments, a narrowband filter radiometer has been constructed for ion detection in the atmosphere. It uses a filter centered at 9.15 mum wavelength with 5% bandwidth, protected by a diamond-like-carbon coated germanium auxiliary filter, and fitted to a standard pyrradiometer. A sensitivity of (29.3+/-0.1) microV/(W m(-2)) has been determined in a laboratory calibration using a blackbody source. Atmospheric experiments show that the filter radiometer, when used with a stable, low-noise amplifier, can respond to cluster-ion fluctuations. The filter radiometer's sensitivity to atmospheric ion changes is (0.47+/-0.05) (mW m(-2))/(ions cm(-3)).
authors.affiliation: Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom. k.l.aplin@rl.ac.uk
authors.forename: K L
authors.initials: KL
authors.lastname: Aplin
authors.forename: R A
authors.initials: RA
authors.lastname: McPheat