REFLECTIONS ON 40+ YEARS OF IONOSPHERIC RESEARCH
A. J. FERRARO
I have been asked by Dr. John Mathews to write a few words about the early days of the Ionosphere Research Laboratory. As a member of the current laboratory, CSSL, I have been given this honor because I have just retired and have been around for a long time. Actually I have just completed 41.4 years of service to Penn State and have been a member of the IRL and CSSL during that time. Remember that the memory fades a bit with time, so while I will attempt to be accurate, those readers that are from the days of IRL can feel free to write to me if something I refer to is not quite correct.
Those of you who have been around for awhile certainly know about IRL and the founder, Dr. Arthur Waynick. You have probably read that the lab was founded in the early 40s and was devoted to the study of the ionosphere. The major sponsor for research funding was AFCRL, known then as the Air Force Cambridge Research Laboratory, and our research monitor was an outstanding ionospheric physicist, Dr. Wolfgang Phister. He would visit the lab about every three months and stay at least two days. I vividly remember having to give a presentation to him for about 15 minutes, as did all staff and students, each time he came for a review. He had great insight and would provide us with some good ideas to follow through. In those days, Art would have us write weekly, monthly, quarterly, and annual reports so we had the material to present to Dr. Phister, but it was still frightening for the students. Those weekly reports were a good idea (now thinking back), and it was a great way to keep up with what everyone was doing in the lab. By Friday noon of each week you were required to hand in a report to the secretary saying what you did during the week and what you planned to do next week. Two to five sentences would do. Upon returning to the lab after lunch, you would find on your desk a compilation of all the reports. It made good reading and would strengthen your understanding of the progress being made by all collectively to dissect the ionosphere.
When I think of all the hi-tech devices we have today - E-mail, FAX, PCs, voice mail, cell phones and laser printers - I wonder how we ever got anything accomplished back then when there was not even a main frame computer on campus. For computations (and some of the wave equations to be solved were horribly complicated ) we used what today would be called a spreadsheet. In the computational lab we had rows of mechanical Monroe calculators and a "computress" sitting at each one. They were given a large spreadsheet-like paper pad with the formula for each cell handwritten at the top with calculations progressing from the first to the last column. On the rows were the initial data and the results of the calculations as they were being processed. Not much different than Lotus or Excel except for speed and accuracy. A solution for a few different starting parameters would take days, as opposed to today's almost instantaneous output from your office PC. Now what did we do with all this spare time while waiting for a result?... THINKING TIME! This is something that now seems to be missing from university life due to the rush of so many things to keep one busy.
In the study of the ionosphere, or more precisely to arrive at the physics and chemistry of the formation of the ionosphere, experimental tools were limited; we had no rockets to "probe" directly the medium being investigated nor did we have satellites to "look down" upon the ionospheric region. We could only rely upon using radio waves to probe that region. For that purpose the Lab had at Scotia Game Lands a large antenna and powerful radio transmitter for sending low frequency waves up into the ionosphere and studying the reflected waves that had been modified by the medium through which they passed. The mystery was to determine what the ionosphere "looked" like from the characteristics of the reflected waves, and that is where the wave equation came into play, for this medium was inhomogeneous, lossy and anisotropic. The Lab spent a lot of time looking for ways to solve these equations, and some of you might remember Dr. J. J. Gibbons who was instrumental in creating new methods of solutions. Maybe some of the readers might remember the large antenna at Scotia; there were eight 250-foot towers in a North-South line evenly spaced with flashing red lights on the towers. It was a nice view at night when driving along route 322, and aircraft reported using the lights as a landmark. The Lab was internationally known for its work with radio probing the ionosphere and by its distinctive blue-covered Scientific Reports which went all over the world. The first Scientific Report was written March 1949 by Kelso on "The Maximum Height of a Radio Wave in a Curved Ionosphere." What I believe to be the last report was #484 written February 1987 by Nisbet and Divany on "Instructions for running the PC Version of the Penn State Mark II Ionospheric Model."
The high-power transmitter was the nerve center of the lab, and several of us were responsible for collecting data on absorption, phase height, virtual height, polarization and ionospheric motions. Much time was spent during the mid 50s by the experimental group trying to perfect the data-taking capabilities (data was recorded on chart recorder paper or film). At the same time the ionospheric physicists were restless, for they wanted "data" to substantiate their new chemical reaction scheme for the formation of the D-region of the ionosphere. I recall Art coming to me after I was working on the instrument for a year and saying it is time to put down the screwdriver and collect data. He was correct, of course, and after collecting a year's worth of 24-hours-per-day data (subject to transmitter and receiving equipment downtime) I was ready to interpret the charts. Fortunately along came the first main frame on campus, PENNSTAC, and solutions to the wave equations came more easily. Finally I arrived at a model of the D-region and received my PhD degree. I remember my advisor, Dr. J. J Gibbons, asking me a good question at my thesis defense; he wanted me to tell him how to estimate the radius of an electron. Although I spent all my research time in computing how many electrons there were in the ionosphere, this was a surprising question. The readers might want to ponder over this. HINT: find the electrostatic energy stored by a spherical charge of unknown radius R and equate this quantity to mc2; finally solve for R.
I joined the faculty of Electrical Engineering in 1959 and continued pursuing the ground-based technique of measuring the D-region of the ionosphere. However I realized that the way we had been doing the experiment lacked height resolution while other techniques like the rocket probe measurement claimed to have improved upon the older ground-based methods. At this point I became interested in the cross-modulation, experiment or amplitude wave interaction, as it was also called. This technique was known for some time but was never extensively used as a diagnostic tool. It seemed to provide the much needed height resolution, so Hai-Sup Lee and I researched this idea and struck upon an improvement which we called radio wave phase interaction. In simple terms, we found another parameter to be measured that would insure better accuracy in the derived electron density profiles that would be even faster to collect and interpret the data.
To test this concept would require an entirely new transmitting facility and funds were not yet available. So we did some modifications to the high-power low-frequency transmitter that was sort of on its "last legs" and Steve Weisbrod (my first PhD student) tackled the problem as his thesis topic. He put in countless hours looking at the theory and designing the special receiving equipment, transmitters and antennas. He was well rewarded, for at 2 a.m. in 1962 at Scotia, he and I watched with amazement as the chart recorder was tracing out the first measurement of the detection of phase interaction. That was the beginning of my career in the area of ionospheric modification .
From there we went out with a proposal to the Office of Naval Research requesting the funds for a completely new installation to measure wave interaction, and we were blessed to receive the funds. In the early 60s $300,000 was a large grant. However, the antenna installation cost $60,000, and the transmitter company designed and built a one-of-a-kind for $75,000. Still a lot was left for a flurry of student theses and numerous URSI presentations. All was not rosy for we were competing with the Canadians using a technique called partial reflections. Jack Belrose had his facility in Ottawa, and his results and ours never seemed to agree; this was somewhat understandable since his latitude was higher than ours and theory would say that there should be a difference, but the arguments continued and URSI presentations ended up with a lot of heated discussions. Fortunately a wave interaction facility could be easily expanded to do partial reflections but not the other way around. Now we found ourselves doing two experiments and trying to decide which was better and more accurate. We concluded that wave interaction was a superior method, and we continued to expand upon that concept. Cohen, Portelli, Newman, Tomko, Richardson, Sulzer, Volz, Kissick, Baran, Breakall, Spooner, and Resnick were some of the students that helped the partial reflection and wave interaction experiments reach completion.
Now came another surprise. The high-power transmitter was beginning to cause interference to many other radio services. Our station, KA2XPO, being experimental, was sharing a frequency band with other more important services like the Canadian forest fighters and the Coast Guard on the Chesapeake. We set up a hot line, and if there was interference we would shut down. Soon managing interference problems was more time consuming than doing the research, and the facility had to shut down. However, we took this opportunity to explore doing this experiment at the Arecibo Observatory in Puerto Rico which had the incoherent scatter facility but it would not work too well at low altitudes, so Arecibo was a natural place to set up. Again we scrounged existing equipment and modified it including the log periodic antenna hung over the 100 foot dish for the main wave interaction antenna. This was not satisfactory to the radio astronomers who would have to wait for our 2-week experiment to conclude. The method did work, but there was a need for a new antenna devoted to wave interaction or ionospheric heating, as it was called then. Jim Breakall and I came up with a neat antenna farm of 32 log periodic antenna elements which was accepted by the observatory and built. The facility was in use for a number of years by several scientists besides Penn State, but it met with its destruction during the last hurricane that struck the island.
One major experiment that I performed at Arecibo that paved a new direction for my research activities was to heat the ionosphere from the high-power wave interaction transmitter in an extremely low frequency mode that would modulate the natural current system flowing overhead of the antenna beam. This modulated current system was in effect an antenna, and it would radiate at this extremely low frequency (ELF); hence a wireless (one without wires) antenna was formed in the lower ionosphere. The importance of this result was that one could more easily generate ELF waves which would reach the lower depths of the sea to communicate with submarines. Obviously the Navy would have interest in this concept. My students that played an important role with this idea were Allshouse, Carroll, Lunnen, and Long, who were always accompanied by Tom Collins, who provided the real technical know-how to make these experiments a success.
The Navy was funding the development of a new heater facility in Fairbanks, Alaska, since the current system was more intense and ELF generation could be much stronger and might find actual applications to Navy communications systems. The facility was operated by UCLA, but Penn State was awarded a large contract to make the facility produce data and to access the capabilities of this facility known as HIPAS (High Power Aurora Simulator) - first set up to cause man-made northern lights - but that was not feasible. We showed that one could almost always generate ELF signals, but the strength was strong during electrojet activity. We also showed that we could send digital data (although at a low baud rate) by phase shift keying the ELF carrier. Our mobile receiving van was out several hundred miles from the HIPAS source, and we managed to receive these ELF signals. An interesting experiment we did was to create two ionospheric antennas in the D-region spaced one-half wavelength apart and phased either 180 degrees of 0 degrees in phase, creating what antenna experts would know as the end fire and broad side two element array. Our mobile van confirmed that we could make arrays of wireless antennas. Although two elements were the limit for the HIPAS facility, it did suggest that for a much larger facility one could perhaps construct a larger array of ELF elements and steer the beam of ELF radiation in desired directions. This was a first-time demonstration of this effect which could have bearing on future Navy system submarine communications, thanks to the efforts of Baker, Werner, Zain, Li, Sonsterby and Collins.
Now to save space I will take some gigantic leaps in time to conclude this discussion. Realizing the importance of ELF generation and ionospheric heating in general, the Navy requested proposals for the feasibility study of an even larger heater facility; effective powers of 10 Gigawatts over a large range of HF frequencies were in the specifications. At that time the antenna to handle this power and bandwidth and to be able to steer the heater beam in arbitrary directions was unknown. Penn State was one of three to be picked for the three-month feasibility study along with Raytheon and APTI (Arco Power Technology Inc.). Three months and $300,000 kept us up many nights, but we arrived at a rather unique facility of wide-band antenna and a modular approach to solid-state transmitters to meet the specs; I also recall we had suggested an underground control center that did raise eyebrows since environmentalists do like to disturb the permafrost. Our unique contribution involved the FIPA (frequency independent phased array) invented by Jim Breakall. It really solved most of the wide-band requirements. Unfortunately our antenna did not win since it was a new concept and the funding agency did not want to take on technological risk, but APTI did win with their straight forward array of closely spaced dipoles which later did cause some difficulty in "tuning" up the array. I said it was unfortunate that we did not win, but maybe we were fortunate for how could a University supervise such a large construction program from 5000 miles distance? However, APTI, asked use to join them as subcontractor and design their antenna, which we gladly accepted. This work was done from ARL with the aid of Lunnen, Werner, Breakall, Groff and myself. We were successful, and we turned our design over to APTI; they began the construction and built several stages of the antenna and continue to expand the facility to its final design stage.
My last few years at Penn State turned to different directions; I developed and taught a 400 level course on satellite communications, which was very popular and gave the students something they could use in the real world of industry. My research continued with industry support in antenna design but not for ionospheric heating experiments.
I would be open to comments about items I may have overlooked. You can reach me at AJF4@PSU.EDU. Although I have focused on ground-based methods, the Laboratory is very multi-dimensional and covers many other important aspects. Thanks to all that made my time at Penn State interesting; I hope to see or hear from you often.
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