IIHR's Elastic Lidar, IIHR, College of Engineering, The University of Iowa

Figure 1. Elastic lidar set up in the field.

The IIHR scanning miniature lidar (SMILI) is a small, scanning lidar which uses elastic backscattering to determine the distribution and properties of atmospheric particulates. The lidar operates by emitting a pulse of infrared laser light into the atmosphere. Particulates and molecules interact with the pulse and scatter light back to the lidar. The amount of returning light collected by the telescope is proportional to the particulate content of the air and the amount of atmospheric attenuation. The system is capable of both day and night operation.

The lidar is built into in four carrying cases and uses a portable computer to control the system and take the data. The system is normally transported disassembled to make the system lighter and more portable. It is designed so that assembly may be done by one person in just a few minutes. The compact size of the system makes it possible to set up virtually anywhere, maximizing the uses to which the instrument can be put.

A Nd:Yag laser operating at 1.064 (or 0.532) microns is the laser source. The laser is attached to 25 cm, f/10, Cassegrain telescope. The laser beam is emitted parallel to the telescope after going through a periscope. The telescope-laser system is able to turn rapidly through 200 degrees horizontally and 100 degrees vertically using motors incorporated into the telescope mount.

The system is entirely computer controlled through the use of various cards in the PC. This enables high speed data transfer and control of the scanning motors, which allows the capability to scan rapidly. The system can be operated remotely and also using preprogrammed sequences which require an operator only to start.

The elastic data from the lidar is analyzed in order to quantify the existence, amount, attenuation, and reflective properties of the atmospheric particulates. The determination of backscatter and extinction information from elastic lidars is a classic inverse problem in remote sensing. The ability of the lidar to scan enables the measurement of horizontal winds over an area of nearly 100 km2 using a correlation technique. The small size of the lidar coupled with its fast scanning capability and sophisticated scanning and analysis methods make this lidar unusually capable and versatile.

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Figure 2. An example of the relative particulate distribution in a vertical slice of the atmosphere.

For more information about the IIHR scanning lidar or atmospheric dynamics, please contact Prof. William Eichinger.