Multifilter rotating shadowband radiometer (MFRSR) calibration values for aerosol optical depth (AOD) retrievals were determined by means of the general method formulated by Forgan [Appl. Opt.33, 4841 (1994)] at a polluted urban site. The obtained precision is comparable with the classical method, the Langley plot, applied on clean mountaintops distant of pollution sources. The AOD retrieved over São Paulo City with both calibration procedures is compared with the Aerosol Robotic Network data. The observed results are similar, and, except for the shortest wavelength (415 nm), the MFRSR's AOD is systematically overestimated by approximately 0.03.

A high-resolution and compact wavelength detector capable of resolving very small changes in the spectral information of the incident light is highly desirable for many applications such as Lab-on-Chip systems, biosensors, chip-sized detectors, on-chip fluorescence spectrometry, wavelength shift detectors, interrogations system, etc. In this work we present the simulation and design of a variable interference filter (VIF) constituted by a wedge-shaped Fabry-Perot cavity placed in between two stacks of thin films, forming dielectric reflectors. This device constitutes an optical filter that converts the spectral information in a position dependent signal that can be measured by a photo detector, a PDA or a CCD. We have investigated the performance of the designed VIF depending on its optical properties in order to optimize its geometrical configuration. With the results obtained we intend to fabricate a multi-channel spectral detector that can be used in environmental analysis.