LIS (Lightning Imaging Sensor)
Specification of LIS(Lightning Imaging Sensor)
LIS is designed by a team of H. Christian (NASA) to achieve optical observations of lightning activity from space. It is equipped on TRMM satellite, and it has been operated since November 1997 when TRMM satellite was launched successfully. LIS consists of two main, and one of main systems is CCD matrix with telescope lens. The other is the real time data processing unit on board.
The history of lightning observations from space itself is rather long, and in early 60's when human beings obtained the capability of a spacecraft the project named OSO-2 was conducted. The optical observations and electromagnetic wave observations are well known. The former owns the disadvantage of the difficulty to detect lightning activity in the daytime hemisphere because the intensity of solar optical emission is much stronger than that of lightning. On the other hand the disadvantage of the latter is the lower spatial resolution than the former.
The requirement to reveal the global distribution of lightning activity, seasonal variations and diurnal variations is increasing year by year, and that is why we are forced to have observations of lightning activity for both day and night.
It is known that the temperatures of lightning channels are normally between 20000K and 30000k. That means the lightning channel is believed to be plasma, and we have many atomic line optical emissions. We know lines of H¦Á (656.3nm), Oµ(1) (777.4nm) and Nµ(1) (868.3nm) among various atomic line emissions are intense. Hugh and his staff pay their attention on Oµ(1) line and designed LIS. To detect the emission by lightning discharges in extremely intense back ground signals due to solar emission, LIS is carefully designed with optical filter of its band width 1 nm. LIS owns the 8.5km spatial resolution and 2mseconds time resolution with 128 by 128 CCD matrix and telescope lens. The threshold level for lightning discharge detection is given as 4.7J/m/m/sr by H. Christian and S. Goodman, and they expect 90 % of detection efficiency.
Details of OTD is described on NASA GHCC web pages
Comparison LIS observations with ground base measurements
LIS Observations of Lightning Activity