Hovemere Daytime Filters
Double EtalonThe double etalon has had outstanding success in recent times. The system acts as a superb filter and provides excellent contrast. This has allowed the development of many instruments capable of working under daytime conditions, such as, most notably, the ozone lidar at the ALOMAR research station. A double etalon instrument built by Hovemere produced the first ever ground based daytime observation of the aurora (Rees et al 1999).
A typical double etalon system comprises at least one capacitance stabilised etalon (CSE), and usually two. Hence, the recent development of the CSE has resulted in a double etalon technology that could open up new areas to scientific observations. For example, Lidars have been used to monitor forest fires by detecting smoke particles and then tracking the direction of the smoke. During the day, the sun obscures the observations but with a double etalon system this obscuration can be removed, thus allowing daytime operation.