The Brewer Spectrophotometer as a Powerful Research Tool

The original development of the Brewer spectrophotometer and subsequent upgrades have provided users with pre-programmed routines for making a suite of the most common types of operational measurements, set-up, tests, and calibrations. Preprogrammed routine measurements include global UV scans, Umkehr measurements, measurements of total ozone, SO2, and NO2 using direct sun, zenith sky, or global radiation. Operational tests include standard lamp and mercury lamp tests to set wavelength, wavelength shutter motor test, and dead time test. Calibrations include the slit function dispersion measurement and responsivity calibration for global measurements.

Software operating on the control computer offers interested users the opportunity to develop customized programs to carry out specialized types of measurements and support tests. Customized measurements take advantage of the fact that all operational mechanical adjustments are controlled with stepping motors. Depending on the objective of a specialized measurement, some hardware modification may be required. However, most hardware modifications are relatively minor and fairly easy to implement. For example, a custom filter may replace or supplement an existing filter in one of the three filter wheels. Some of these specialized measurements have been discussed in pervious sections (Bais, 1997; Wardle et al., 1997; Grobner et al., 1998; Grobner and Kerr, 2001; Kerr, 2002; Kerr and Davis, 2007). Other customized measurements include that developed to measure NO2 using an advanced scanning technique (Cede et al., 2006b) and a new method developed to measure tropospheric and stratospheric ozone profiles using sky radiance measurements at multiple viewing angles (Tzortziou et al., in press).

There is further potential for use of the Brewer instrument to explore other possible scientific applications. Pointing capabilities allow the investigation of the dependence of spectral irradiance as a function of direction. Measurement of radiation in the first order of the Mark II instrument (600 nm - 650 nm) could allow the measurement of ozone using the Chappuis band. Measurements could then be made at low solar elevations since ozone absorption is smaller and Rayleigh scattering is significantly less at these wavelengths than those in the UV. A new scan type, called the "group-scan method," has recently been developed (Kerr, 2002) and could be applied to the measurement of NO2 at visible wavelengths, resulting in improved accuracy for measurements of NO2.

Brewer instruments have also participated in numerous scientific field campaigns that are intended to study various aspects regarding atmospheric composition and surface UV radiation. Measurements made by Brewer instruments provide important input to detailed investigations of photochemical and physical processes involved in our understanding of the ozone layer and surface UV radiation. In some cases, special measurements and schedules are developed to ensure critical measurements are made at appropriate times. Contributions made to campaigns include measurements of atmospheric variables such as total ozone (e.g., Kerr et al., 1994; Margitan et al., 1995), aerosol optical depth (e.g., Gröbner et al., 2001), or surface UV radiation (e.g., Bais et al., 2001).

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