TABLA N° 3.10 DIAGRAMA DEL PROCESO DE PRODUCCION DE MIEL DE ABEJA

As new techniques became available for research - particularly the development of large-scale integrated circuits for both analog and digital electronics - huge advances were made in computers, memory technology, and communications. These advances in turn led to major improvements in the ability of scientists to make measurements in atmospheric electricity, display the results, and analyze the data. As new knowledge became

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available, the Lightning Launch Commit Criteria (LLCC) were revised, updated, and improved to increase both launch availability and launch safety.

Among the scientific advances that were made in the early- and mid-1970s, largely as a result of the Apollo 12 lightning incident, were the development of (a) an improved ground-based method for detecting and

displaying cloud electric fields and (b) improved methods for detecting, locating, and displaying both intracloud and cloud-to-ground (CG) lightning discharges. These advances were tested at KSC and were the basis for many of the subsequent improvements in the LLCC.

3.4.5.1 Launch Pad Lightning Warning System (Field Mill Network)

The LPLWS is basically a large-area network of electrostatic field sensors (field mills) that measures the vertical component of the electrostatic field, E, produced by cloud charges aloft, even if those clouds are not producing lightning. The sensors are termed ‘mills’ because they employ a rotating and grounded metallic shutter to alternately cover and uncover a set of insulated stators that respond to E. The amplitude and phase of the AC current flowing to and from the stators is proportional the amplitude and polarity of the local electric field. When an electrified cloud forms overhead or moves into the region from somewhere else, the E field will increase in magnitude and often change polarity. In most cases, E will be large close to the cloud charges and small farther away, so 2-dimensional maps of E will show approximately where the cloud charges are located. If the cloud electric field is measured in conjunction with a weather radar that senses precipitation, the onset of the electric field can be compared with the onset and type of precipitation, the rate of echo growth, and the time-evolution of the cells, thereby improving both the nowcasting (i.e. detection) and forecasting of high fields aloft. When lightning discharges occur, maps and analyses of the lightning-caused changes in E, or ΔE, can be used to determine an approximate location (in 3-dimensions) of the change in the cloud charge (Maier and Krider, 1986; Koshak and Krider, 1989; Krider, 1989).

The unique features of the LPLWS are its large area (approximately 20 x 30 square kilometers), the number of field mills (25 to 33), and the fact that each sensor is mounted (and calibrated) in the same way on uniform sites that are cleared of vegetation. A network such as this minimizes the frequency of false alarms, such as might be caused by a single sensor having an incorrect reading, and also any ‘failures-to-warn’ that might occur if the positive and negative cloud charges are not vertically aligned or if the field seen by a single sensor is masked by intervening space charge. Further details on the implementation and calibration of the LPLWS at the KSC-ER are given in Appendix VII by Michael W. Maier.

Among the first scientific studies that were based on the field mill network were analyses of the electrostatic field changes produced by Florida lightning by Jacobson and Krider (1976) and the overall behavior of E under both small and large storms at KSC by Livingston and Krider (1978). These studies showed that the charge centers inside Florida storms are located at altitudes where the air temperatures are below freezing, i.e. where the environmental temperatures are between about -10 ºC and -20 ºC, and that the time-average values of E are often surprisingly small when averaged over five minute intervals, even under active storms. The finding that the lightning charges are located at subfreezing temperatures lent support to the idea that a non- inductive ice-ice collision process is the dominant microphysical mechanism in cloud electrification (Saunders, 1988; 2008), and the LLCC still rely on this assumption.

3.4.5.2 Cloud-to-Ground Lightning Surveillance System (CGLSS)

KSC has made major contributions to the development of two complementary systems for detecting and locating lightning, the Cloud-to-Ground Lightning Surveillance System (or CGLSS) and the Lightning Detection and Ranging (or LDAR) system. The CGLSS utilizes a network of gated, broadband electric and magnetic field sensors (Krider and Noggle, 1975) to detect the waveform signatures that are characteristic of return strokes, the high-current components of CG flashes (Krider et al, 1976; Herrman et al., 1976). When a proper signature is detected (in the time-domain) at two or more known locations (the antenna sites), the

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coincident times-of-arrival and magnetic directions can be used to compute the point where a return stroke strikes the ground (Krider et al., 1980; Cummins et al., 1998; 2006).

According to a time-domain antenna theory developed by M. A. Uman and his collaborators shortly after the Apollo 12 incident (see for example Uman et al., 1975), the initial peak of the electromagnetic pulse that is radiated by a return stroke is proportional the peak current in the stroke, multiplied by the speed of the stroke propagating up the leader channel, and divided by the distance to the stroke. [Note: this theory is sometimes called the simple ‘Transmission-Line Model’ or TLM because it assumes the current pulse propagates up a straight channel, without distortion, and at a constant speed.] Since the CGLSS measures the peak field and can compute the stroke location, and since the stroke velocities are known and roughly constant, the CGLSS can also provide an estimate of the peak current in the stroke and its polarity.

The first CGLSS system was installed at the KSC-ER between 1 June 1979 and 12 July 1979. It was a prototype consisting of three medium-gain magnetic direction-finders (DFs) and was installed as part of the Federal Evaluation of Lightning Tracking Systems (FELTS). This system was subsequently purchased in February 1981 with joint funding provided by NASA and the Air Force. Later upgrades were performed as described in Chapters 4 and 5.

3.4.5.3 Lightning Detection and Ranging (LDAR) System

The first LDAR system was developed at KSC by Carl Lennon and associates after a design described by Proctor (1971). It contained seven broadband VHF radio receivers that were deployed at the sites shown in Figure 3.4.5-1 and were precisely time-synchronized, initially using microwave communications links and later GPS timing. Each site received VHF radiation at 66 MHz, logarithmically amplified the signal, and then transmitted the time and key signal parameters to a central station where the source locations were computed [Lennon and Maier, 1991; Maier et al., 1995]. The 3-D locations of the sources of lightning VHF pulses are computed using the differences in the times-of-arrival of the signals detected at the different receiver sites. Since the main sources of VHF radio emissions are the processes associated with air breakdown, the LDAR system detects primarily the in-cloud portions of CG flashes, leader processes, and intracloud discharges. Today each LDAR receiver site operates automatically and is powered by batteries that are recharged by solar panels. The first LDAR system was developed by the KSC Instrumentation and Measurements Branch, and the current one is operated and maintained by the ER Technical Services Contractor. The 45 WS receives and evaluates the LDAR data 24 hours a day, 7 days a week. For further details on the evolution of the LDAR system and other instrumentation at the KSC-ER, see Boyd et al. (1995), Harms, et al.(1997; 1998; 2001) and Roeder et al.(1999).

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Figure 3.4.5-1 KSC LDAR Sites

3.4.5.4 U.S. National Lightning Detection Network (NLDN)

Data from the U.S. National Lightning Detection Network (NLDN) (Cummins et al., 1998, 2006;

Cummins and Murphy, 2009) have been used to detect and track CG lightning flashes beyond the

range of the CGLSS and LDAR systems since the early 1990s. The NLDN sensors are similar to

those used in the CGLSS except that they have higher gains and larger distances between the sensors.

The coincident data from two or more sensors are collected and processed in real-time by a network

control center in Tucson, Arizona, and the GPS time, location, and polarity of each lightning stroke,

together with an estimate of its peak current, are provided to the KSC-ER in real-time. For further

information about the NLDN and its history, see Cummins and Murphy (2009).

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