JOURNAL OF GEOPHYSICAL RESEARCH, Vol. 106, Number D24, Page(s) 33499-33509, DECEMBER 27, 2001

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Figures and Plates

Figure 1. Photodiode detector responsivity versus wavelength. The peak detector responsivity is near 0.85 m.

Figure 2. Photodiode detector calibration curve. Abcissa gives digitizer counts. Ordinate gives irradiance in watts per square meter.

Figure 3. Intertrigger delay (ordinate) as a function of event number (abcissa) for 10,000 events recorded in early October 1999. The minimum intertrigger delay is consistently 4.37 ms and is due to the time required to rearm the PDD sensor.

Figure 4. Examples of the three basic types of signals observed by the PDD. The abcissa gives time in microseconds and spans 1.9 ms. The ordinate gives the signal irradiance in watts per square meter. (a) A typical signal attributed to lightning. (b) A signal attributed to instrumental electronics noise, or to glint off of spacecraft or Earth surfaces. (c) A signal typically attributed to the passage of energetic particles through the photodiode.

Plate 1. A geographic map showing NLDN and PDD events over the Atlantic Ocean, off the northeastern coast of North America. The oval represents the time-integrated PDD FOV for a nearly 6-min period of time. Black crosses denote 325 NLDN event locations during the same period. Red diamonds mark 61 NLDN events for which a PDD event detection occurred within 500 s of the NLDN event time. See text for additional details.

Figure 5. Distribution of PDD-NLDN event delays in microseconds for 4439 PDD-NLDN event pairs temporally correlated within 10 ms. The PDD event times were first corrected to account for the slant path delay between the NLDN source location and the satellite location. The histogram bin size is 10 s.

Figure 6. Sequence of six consecutive PDD events detected over the Pacific Ocean in October 1997. The abcissa gives time in seconds and spans 60 ms. The ordinate gives irradiance in watts per square centimeter. Note that the signals exhibit complex structure and are also truncated by the finite PDD record length. See text for discussion.

Figure 7. Distribution of PDD event peak powers as recorded at a nominal satellite altitude of 825 km. The histogram bin size is about 3 10 ^-6 W m ^-2. The solid curve gives the distribution for all internal trigger, night/slow compensation mode events. The dotted curve gives the distribution of down-selected events such as is shown in Figure 4a. See text for description of the down-selection process. The median peak power observed on orbit is 1.3 10 ^-4 W m ^-2.

Figure 8. Distribution of PDD event estimated source optical energies. The histogram bin size is 10 kJ. The abcissa gives optical energy in joules, and the ordinate gives the relative occurrence frequency. The solid curve is for all internal trigger, night/slow compensation mode events. The dotted curve is for the population of down-selected events as is discussed in Figure 6 and shown in Figure 4a. The optical source event is assumed to occur 825 km below the satellite, and the signal is assumed to experience no atmospheric attenuation.

Figure 9. Distribution of PDD signal effective pulse widths. The histogram bin size is 20 s. The abscissa gives the effective pulse width in microseconds. The ordinate gives the relative occurrence frequency. The solid curve applies to all internal trigger, night/slow compensation mode events that have a character like that shown in Figure 4a. The median effective pulse width for this population is 592 s. The dashed curve is derived from a down selection of the population represented by the solid curve for PDD events associated with NLDN-reported CG strokes (median effective pulse width of 604 s).

Figure 10. Relationship between effective pulse width and estimated peak optical power at the source as observed by the PDD. The median effective pulse width as a function of estimated peak optical power is represented by the triangles. The top and bottom of the error bars represent the 90th and 10th percentiles of effective pulse width. There is a clear trend for the median effective pulse width to decrease with increasing peak optical power.

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