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Detection Instruments

[ALDF Image]Advanced Lightning Direction Finder

These sensors detect cloud-to-ground lightning strikes and determine their location by triangulation of two or more lines of bearing. An ALDF automatically detects more than 90% of all cloud-to-ground lightning occurring within a range of 100 km. Other lightning, such as cloud-to-cloud and intracloud lightning, is ignored. The National Lightning Detection Network (NLDN) is a network of more than 130 of these ALDF sensors.

 

 


[LDAR Image]Lightning Detection and Ranging (LDAR)

Located at the Kennedy Space Center, the LDAR consists of seven antennas that detect electromagnetic pulses at 66 MHz, which allows it to detect 99% of all flashes (both intracloud and cloud-to-ground flashes) within 10 km of the antenna network. The accuracy of source locations is a function of position relative to the receiving array, generally decreasing (particularly along the radial axis with respect to the array center) with distance. The RMS error for LDAR lightning source locations varies from 100 meters inside the network to about 10 km at a range of 90 km (about 1/3 the width of the Florida peninsula).

 


[KSC FM Image]KSC Electric Field Mill Network

Thirty-one advanced field mills developed by NASA/MSFC are deployed at sites around the Kennedy Space Center (KSC) and Cape Canaveral Air Station provide data on lightning activity and surface electric fields induced by charge aloft. This data helps forecasters determine when electric charge aloft may be sufficient to create triggered lightning during launch, and to determine when to issue and cancel lightning advisories and warnings.

 


[Airborne Electric Field Mill Image]Airborne Electric Field Mill

 

In several field campaigns, these field mills have been installed on the top and bottom of a DC-8 and an ER-2 aircraft. With this configuration, the field mills are used to measure the vertical component of the electric field as the aircraft flies in the vicinity of electrified clouds. The dynamic range of these instruments extends from the fair weather fields (a few tens of V/m) to large thunderstorm fields (thousands of V/m). Using these field mills, it is possible to detect both intracloud and cloud-to-ground lightning from the abrupt electric field changes in the data. The field mills were developed by NASA/MSFC.

 

 


[Airborne Conductivity Probe Image]Airborne Conductivity Probe

During numerous flights, a conductivity probe has been installed on the superpod nose cone of the ER-2 aircraft and has been used to measure the conductivity of the atmosphere. The probe consists of a pair of Gerdien capacitor type sensors so that the contributions to the total conductivity due to positive and negative ions are obtained simultaneously throught each flight. Storm electric currents have been derived using electric field and air conductivity measurements.

 

 


[Airborne Optical Pulse Sensor Image]Airborne Optical Pulse Sensor

The optical pulse sensor consists of a photodiode at the focus of a wide angle field-of-view lens, and was used to observe the bright flashes of light produced during a lightning discharge. During the mid 1980s, this instrument was flown on a high altitude aircraft to observe lightning from above cloud top. A bandpass filter was installed at the front of the lens and was used to pass one specific lightning spectral line, such as the neutral atomic oxygen line (777.4 nm) or the neutral atomic nitrogen line (868.3 nm).

 

 


[Broadband Spectrometer Image]Broadband Spectrometer

This instrument is an Ebert spectrometer which was used to measure the spectral characteristics of lightning discharges. The spectral range of this instrument is from below 600 nm to almost 900 nm (infrared spectrum). This instrument was also flown on a high altitude aircraft during the mid 1980s.

 

 


[Broadband Spectrometer Image]Fly's Eye GLM Simulator (FEGS)

FEGS is an airborne instrument designed to provide cal/val measurements for GLM from high altitude aircraft. It consists of a 5 x 5 array of telescopes each with a narrow passband filter to isolate the 777.4 nm neutral oxygen emission triplet radiated by lightning. The telescopes will measure the optical radiance emitted by lightning that is transmitted through the cloud top with a temporal resolution of 10 μs. When integrated on the NASA ER-2 aircraft, the FEGS array with its 90° field-of-view will observe a cloud top area nearly equal to a single GLM pixel. This design will allow FEGS to determine the temporal and spatial variation of light that contributes to a GLM event detection. In addition to the primary telescope array, the instrument includes 5 supplementary optical channels that observe alternate spectral emission features and will enable the use of FEGS for interesting lightning physics applications.

 


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