Abstract
The Spallanzani’s studies on bats and the sophisticated acoustic signals used by bats to localize their prey are a good introduction to some modern radar techniques and systems, including: pulse compression, coherent chains, phased arrays, array processing and antenna side-lobes suppression, weather monitoring, automotive and thru-the-wall applications, as well as radar research facilities.
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Notes
- 1.
Giovanni Pascoli was born in San Mauro di Romagna (presently, San Mauro Pascoli, Forlì-Cesena) on December 31st, 1855 and died in Bologna on April 6th, 1912. Both Baudelaire and Pascoli paid much attention to the night birds of prey: the first one to the appearance of owls, the second one to the song of the scops owls.
- 2.
The bats, mammals of the Chiroptera order, are very useful to the ecosystem as predators of mosquitoes (a bat can eat as much as one mosquito every 10 s, and thousands per night).
- 3.
Lazzaro Spallanzani (January 10th, 1729–February 12th, 1799), abbot and professor at the University of Pavia, a great biologist (mostly famous for its research in the field of reproduction), was able to relate the consumption of oxygen with the tissue respiration, worked the artificial insemination in dog, showed the action of gastric juice and did many other discoveries. The most important of them was probably having refuted experimentally the thesis of spontaneous generation. Last but not least, Spallanzani first understood that bats orient, and localize their prey, with ultrasound.
- 4.
When Spallanzani caught, in the bell tower, some bats that he had blinded, and then freed, a few days before, he found in their stomach a myriad of insects, just as in the stomach of other (not blinded) bats: the blinded bats could perfectly orient themselves in the dark and succeed in capturing their prey.
- 5.
[Gri 59] is a delightful book readily available also on line.
- 6.
The North America Society for Bat Research (NASBR) has organized since 1970 an annual Conference, the North American Symposium on Bat Research, associated with a prize, the Spallanzani Award, which allows the participation of scholars not coming from the United States, Mexico or Canada.
- 7.
A typical bat signal is available at: http://dsp.rice.edu/software/bat-echolocation-Chirp.
- 8.
Among them, the patent N. 768068 by E. Huttman dated March 22th, 1940 and the paper by R. Krönert on 1942.
- 9.
The main patents were by Dicke (January 6th, 1953, N. 2624876) and by Darlington (May 18th, 1954, N. 2678997, entitled Pulse Compression).
- 10.
In summer 1959, based on the P-12 Radar System, a prototype of VHF-band radar with LFM pulse compression was built and tested under the leadership of Y.D. Shirman, with a pulse duration of 6 microseconds and a spectrum width of 5 MHz. After processing, range resolution improved 30 times without practical decreasing in range performance.
- 11.
Pat. N. 149134, 146134, 146803 and 152487.
- 12.
An example is the P-12 “Yenisei” (NATO name “Spoon Rest”), a Soviet early warning, ground-based VHF radar with a maximum range of 200 km, and altitude up to 25 km, modernized, exported to various nations including Egypt and Serbia, and used in the Vietnam War as well as in several conflicts in the Middle East. It is a three-dimensional monostatic radar, in which azimuth is scanned mechanically by the antenna at 10 r.p.m while the target elevation is determined by phase comparison between upper and lower antenna portions. P-12 has been replaced with the more modern P-18 (NATO name “Spoon Rest D”).
- 13.
As a matter of fact, the real aim of the large US investment in Stealth aircraft was not so much to directly attack the Soviet, but rather, to force them to sustain huge costs to make their defense systems effective against such threats, leading to a potential economic collapse. In fact, let us consider a reduction of the radar cross section by a figure of a thousand: the radar range in free space is reduced by a figure of 5.6. This means that, in order to maintain an effective line of air defense for the vast Soviet land, the number of surveillance and warning sites (and radars) has to be multiplied by about six, with hardly bearable costs.
- 14.
The JY-27 (somewhat similar to the Russian 55Zh6ME radar) is claimed to be operational and to have a maximum range of over 435 km, and the following operational modes: omnidirectional surveillance, sector search and missile early warning. The estimated number of antenna elements is 480.
- 15.
Two programs (http://www.darpa.mil/Our_Work/STO/Programs/Multifunction_RF_%28MFRF%29.aspx) of the US Defense Advanced Research Projects Agency (DARPA), i.e. the Multi-Function Radio Frequency (MFRF) and the Video Synthetic Aperture Radar (Visars) are in progress in 2012 for radar imaging in the band of 90 and 230 GHz, respectively. MFRF is a intended for guidance, and landing, of helicopters in critical conditions of visibility, while Visars, that has to be integrated in the standard electro-optical/infrared head of an aircraft, aims to provide radar images with 20 cm resolution and update rate 5 times per second, fast enough to track a person or a land vehicle in motion.
- 16.
In reality, pulse compression was used in an extended way only after W.W.II, which was likely due technological limitations.
- 17.
The U-2 was able to fly up to 70,000 feet, more than 21 km altitude; according to the experts USA?which were wrong?such a high elevation should have protected it from the Soviet surveillance systems and missiles.
- 18.
According to some sources, this method, developed for the airborne SAR, has also been applied to the satellite-based SAR. The film was sent to the ground with small rockets and parachutes.
- 19.
In the technical literature the digital generation of plots and tracks is called Automatic Detection and Tracking (ADT); automatic detection involves the definition of a threshold, which must adapt itself to the variations of the disturbance in order to maintain a constant probability of false alarm, that is, a constant false alarm rate, or CFAR processing.
- 20.
The MTI cancellers operate with one or more delays of one pulse repetition period each, i.e. of the order of a millisecond, corresponding to a target range about a hundred km. Therefore, to implement the related delay, in the 1940s and 1950s the radar signal was transduced into an acoustic wave, and the delay lines were implemented in water, mercury or quartz: the physical length was thus reduced by the ratio of propagation speeds, in practice by five orders of magnitude. When the total acoustic path length was relatively large, e.g. order of one meter, multiple paths permitted the use of relatively compact structures.
- 21.
The MTD processor is due to the work, which took place from 1969, of a team from the Lincoln Laboratory of the MIT, led by Charles E. Muehe .
- 22.
The operating frequency of Wassermann, same as the Freya, was in the 125 MHz band. Its 100 kW power permitted maximum ranges up the 300 km.
- 23.
For both Wassermann and Mammut the transceiver and the radar operators were housed in large underground bunkers, see [Rus 94].
- 24.
Atlantic Pact, Washington, April 4th, 1949.
- 25.
Basically: long-range stratospheric missiles, strategic bombers and nuclear-powered submarines with nuclear warhead missiles.
- 26.
This defense line was built in less than three years (1955–57) in a particularly difficult environment such as the polar one (beyond the 69th parallel).
- 27.
This S band, solid-state experimental phased array radar (ELRA: ELectronic steerable RAdar), built and operated by the German Research Institute FGAN-FFM (now, FGAN-FHR) in Wachtberg, near Bonn, allowed, from the early 1980s, some of the former demonstrations of the concepts of adaptivity in arrays and of digital beam forming. In modern radars, the number of array elements may be of the order of 10000, with a subarrays number in the order of 100.
- 28.
In an airborne radar the motion of the platform, in combination with the presence of the antenna side lobes, widens the Doppler spectrum of the clutter and shifts its peak on non-null frequency values, making the detection of targets, with the radar antenna pointing down, particularly difficult when they are at a lower altitude than the platform.
- 29.
AMDR will be a successor of the Dual-Band Radar for the DDG 1000 Zumwalt class and the forthcoming Gerald R. Ford class super-carriers in order to replace several different radars. It is expected that the first AMDR installations will take place in 2019, with orders in 2016, on the ships (DDG 123) of the type now mounting the Aegis Combat System.
- 30.
The final multifunction solution, whose cost/effectiveness is still to be evaluated and whose convenience is still to be defined, is of course the integration into a single antenna of three basic functions: radar, electronic warfare and communications. One may imagine that these new types of sets could be employed, inter alia, on future UAV/UAS (Unmanned Aerial Vehicles/Systems) for ISR (Intelligence, Surveillance, Reconnaissance) or strike missions.
- 31.
The most used terms are: weather radar, meteorological radar.
- 32.
The first record on the detection of rain echoes dates back to February 7th, 1941 at the Radiation Laboratory (but probably others happened in the United Kingdom in 1940). The first American publication concerning the weather radar is due to Bent, 1943, entitled: “Radar Echoes from Atmospheric Phenomena”. PPI radar images of precipitation obtained in the Second World War were of great interest: for example, it was understood that the "hook" shape indicates a tornado type storm with possible hail.
- 33.
The so-called U.S. Basic Weather Radar Network began to grow in 1947 including the first WSR and other radar sets of the U.S. Air Force and of governmental agencies. In the USA, the first purposely designed radar for meteorological usage was the AN/CPS-9 Storm Detection Radar, produced by Raytheon.
- 34.
On April 5th, 1956 at 14:00 on the display of the weather radar of the A&M University, Texas, images appeared of echoes shaped as a hook. The meteorologists of the University called the Bryan Police Department and the College Station School District to inform them of the imminent arrival of some tornado. The school decided to retain the students to shelter after normal closing hours. This timely action probably saved many lives.
- 35.
WSR means Weather Service Radar, and the two digits following the letters indicate the starting year of the relevant programme.
- 36.
Of course, but non-specific of radar meteorology, another fundamental progress was the application of the techniques of digital signal processing and acquisition, recording and display of the results, often called "products", and finally the control of the radar operation by a computer.
- 37.
In May 1973 a tornado struck Union City, west of Oklahoma City. The experimental S-band Doppler radar of the National Severe Storm Laboratory has allowed researchers to follow the entire life of the phenomenon. In particular it was possible, for the first time, to observe the rotation which characterizes the early forming of the tornado. This fact, along with others, has convinced the National Weather Service of the importance of the information of the radial velocity for the prediction of extreme events.
- 38.
According to the style of the US Administration, this is an initiative called Tri-Agency involving Department of Commerce (DOC), Department of Defense (DOD) and finally Department of Transportation (DOT); similar programs allow for the development of equipment, systems, services common to different operational realities, with significant cost savings.
- 39.
See the Web site of the Indian Meteorological Service: http://www.imd.gov.in.
- 40.
Among them, four are of European design (Gematronik 1500 S) and one of Indian design.
- 41.
It has been operational since 2004 in a site about 100 km north of Chennai; a few other sets have been ordered from the manufacturer, Bharat Electronics Limited (BEL), [Mah 11].
- 42.
The Doppler measurements of precipitation are basically two: the mean radial velocity, derived from the first moment of the Doppler spectrum, and velocity dispersion, derived from its second moment.
- 43.
A recent reference with an overview of the problem is [Gor 06]. Until now researchers have made their analytical assessments as if the drops were ellipsoids (of which it is possible to calculate the radar cross-section).
- 44.
For example, by introducing, in addition to the reflectivity Z (measured in the horizontal polarization), the ratio of the received power in horizontal polarization and that in vertical polarization, called differential reflectivity or ZDR.
- 45.
In fact, snow and hail have ?polarimetric signatures? different from rain, due to the different shape of hailstones, snowflakes and drops. The same occurs for the sources of disturbing echoes, such as swarms of insects, birds and, in the case of pointing to low elevation, surface clutter due to the land features and the man-made ones (e.g. buildings, trellis and various infrastructures, including the particularly harmful wind turbines often grouped into wind farms).
- 46.
The first NEXRAD radar transformed into a polarimetric radar was the one at the Air Force Base of Vance, Oklahoma, fully operational since March 3rd, 2011.
- 47.
These reflectors also allow the boat to be more visible by navigation radars and coastal radars, see also: http://www.echomax.co.uk/Echomax_Forward.htm.
- 48.
Some prototypal embodiments were made in the USA around 1970 by Varian Associates together with the Chelmsford MA, and one of them was shown in Detroit, but the Detroit Three (Ford, General Motors and Chrysler) were not interested, probably because of potential liability matters more than because of any technical aspect.
- 49.
The typical specifications of late 1990s were: pulsed emission in the range 76–77 GHz, with bandwidth up to 500 MHz and effective peak radiated power (EIRP) up to 20 W, mean power less than 10 mW and antenna beam width less than 4° in elevation and 15° in azimuth.
- 50.
Further functions have been proposed such as assistance to the lane change, alarms to prevent the opening of the doors in the presence of arriving vehicles, proximity alarms for pedestrians and even more.
- 51.
The European Telecommunications Standards Institute (ETSI) is an independent body and a not-for-profit organization responsible for the definition and distribution of standards in the field of telecommunications in Europe. To be mandatory, the standards must be accepted and promulgated by European (European Commission) or by national Authorities.
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Galati, G. (2016). Scops Owls and Bats—Recent Radar Developments. In: 100 Years of Radar. Springer, Cham. https://doi.org/10.1007/978-3-319-00584-3_9
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