LIDAR CONSTRUCTION
The construction of the system was completed in three different phases.
PHASE 1- The first phase of the system was simple, consisting of one transmitting and one receiving telescope. The dynamic range of this system was limited because of the use of a single receiving telescope. The receiver filter was inexpensive and operated at ambient temperatures. An inexpensive digitizer was also used. These components made the system easy to align, easy to keep in alignment, and easy to operate.
PHASE 1- The first phase of the system was simple, consisting of one transmitting and one receiving telescope. The dynamic range of this system was limited because of the use of a single receiving telescope. The receiver filter was inexpensive and operated at ambient temperatures. An inexpensive digitizer was also used. These components made the system easy to align, easy to keep in alignment, and easy to operate.
PHASE 2 -The initial design was improved by adding a second, 2-inch diameter short-range receiver and using the original telescope as a long range receiver. We also reduced the bandpass of the filter by a factor of 10 and tuned it using a filter oven and controller. These two changes reduced the amount of sky background light reaching the detector by almost two orders of magnitude and permitted daytime measurements. A higher quality digitizer was also used to improve the quality of the data.
PHASE 3- Depolarization capability will be introduced that will permit study of microphysical properties (e.g., distinguishing ice crystals in cirrus clouds from spherical drops in water clouds). PHASE 3 is in progress. The polarizer has been installed, is being tested, and the software is being created to run the polarizer automatically with a computer program in Labview.
Each phase is expected to take approximately 1 year. Various different kinds of measurements (e.g., on various properties, sources, and composition of the planetary boundary layer) will be possible with this newlidar system. After PHASE 3 has been completed, the instrument will be suitable for an even broader range of studies, (e.g., the structural composition of clouds and pollutants). However, even with PHASE 3 in progress, several atmospheric studies can be made with the PEARL.