The GEPAN – SEPRA Report

Appendix 1: Official UFO Investigations in France: the GEPAN/SEPRA Project


  For more than 20 years, the French space agency has conducted a non-military but official investigation into UFO reports. In its first phase, the project was named GEPAN and its focus was primarily on UFO reports. Subsequently, the project was renamed SEPRA and was assigned a more general responsibility for studying all atmospheric reentry phenomena. In the body of the report, we have for convenience referred to the project as “GEPAN/SEPRA.” This appendix gives a brief summary of the history, mission, operations and achievements of this project.

The French space agency is known as CNES (Centre National d’Études Spatiales). It was founded in 1962 to conduct French space activities on a national basis and also in the context of the European Space Agency (ESA) or of other international collaborations. CNES currently has 2,500 employees. The CNES headquarters are in Paris but its technical center is in Toulouse.

GEPAN (Groupe d’Études des Phénomènes Aérospatiaux Non-identifiés – Study Group for Unidentified Aerospace Phenomena) was established as a department of CNES in Toulouse in 1977. At that time, its head was Dr. Claude Poher, who had already performed statistical analyses of files containing several thousand observations worldwide (Poher, 1973). CNES set up a scientific advisory board comprising astronomers, physicists, legal experts and other eminent citizens to monitor and guide GEPAN’s activities.

The first tasks undertaken by GEPAN were:<ul

 To establish data collection procedures in conjunction with the Air Force, civil aviation authorities, the Gendarmerie (French internal police), meteorological offices, the national police, etc.


  • To conduct statistical analyses of eye-witness reports.
  • To investigate previously reported cases.

    These initial studies led to the following conclusions:

    • Those events that remain unexplained after careful analysis are neither numerous nor frequent.
    • The appearance of some reported phenomena cannot readily be interpreted in terms of conventional physical, psychological or psycho-social models.
    • The existence of a physical component of these phenomena seems highly likely.

    Following these initial steps, GEPAN undertook to develop a more theoretical but rigorous approach to these studies. It was clear at the outset that it would be necessary to consider both the physical nature and the psychological nature of the phenomenon. In order to fully understand a witness’s narrative account, it was necessary to consider not only the account but the psychology and personality of the witness, the physical environment in which the event occurred, and the witness’s psycho-social environment.

    GEPAN negotiated agreements with the Gendarmerie Nationale, the Air Force, the Navy, the meteorological offices, police, etc. These negotiations led to procedures by which these organizations provided GEPAN with relevant reports, video tapes, films, etc., which were then processed and analyzed either by GEPAN or by associated laboratories. However, from 1979 on, GEPAN worked mainly with reports from the Gendarmerie since these reports proved to be best suited for GEPAN’s purposes.

    GEPAN developed a classification system to reflect the level of difficulty in understanding the reports:

    Type A: The phenomenon is fully and unambiguously identified.

    Type B: The nature of the phenomenon has probably been identified but some doubt remains.

    Type C: The report cannot be analyzed since it lacks precision, so no opinion can be formed.

    Type D: The witness testimony is consistent and accurate but cannot be interpreted in terms of conventional phenomena.

    Reports of Type A and Type B were further subdivided into astronomical, aeronautical, space, miscellaneous, and identified. GEPAN carried out statistical analyses aimed at classifying cases according to sets of physical characteristics.

    Two types of investigations were carried out on individual reports:

    • Mini-investigations, that were applied to cases of limited significance; and
    • Full investigations, that were applied to unexplained cases (Type D) in which effort was made to obtain as much information as possible, including gathering and analyzing physical and biological evidence.

    During the GEPAN phase, the project initiated several lines of research involving other laboratories and consultants. These were aimed at seeking a possible basis for modeling unexplained aspects of UFO reports, as well as seeking new techniques for the more active investigation of UFO events by the development of detection systems. These research topics included:

    • Research on possible magnetohydrodynamic propulsion systems;
    • Study of facilities to collect unexpected atmospheric phenomena on a worldwide basis, that led to the proposal of the Eurociel Project to develop a network of ground stations equipped with wide-angle observation systems and powerful real-time processing algorithms;
    • Methodology for image analysis (photographs, videos, etc.); and
    • Study of aeronautical cases, especially radar-visual cases.

    In 1988, GEPAN was replaced by SEPRA (Service d’Expertise des Phénomènes de Rentrées Atmosphériques – Atmospheric Re-entry Phenomena Expertise Department). M. J-J. Velasco, who had been a member of GEPAN since the very beginning, took charge of this new project that was then assigned a wider mission. This new project was called upon to investigate all re-entry phenomena including debris from satellites, launches, etc. However, the budget was drastically reduced so that research into UFO reports could not be maintained at the earlier level. Nevertheless, all existing official procedures concerning data collection have been maintained to ensure continuity in receiving reports.

    After 21 years of activity, the GEPAN/SEPRA files now contain about 3,000 UFO reports supplied by the Gendarmerie. About 100 of these reports were found to justify specific investigations. Of this number, only a few cases remain unexplained today.

    There have been attempts by SEPRA to increase the scope of the project at least to a European level, but this has not yet been successful. One of these attempts was the “Eurociel” project: the basic concept was to implement two sets of wide-angle optical detection stations, sited some tens of miles apart following a parallel of latitude, each station to be equipped with CCD-type cameras, with a minimum of one in the visible and one in the infrared. The output from these cameras would feed data into a microcomputer that triggers recording of the data when the computer determines that a change has suddenly occurred. The data from all these stations would be stored in a central facility to permit the calculation of trajectories. Such a system could detect lightning, meteors, unknown satellites, and other known or unknown phenomena.

    During the GEPAN phase, the project produced many reports and investigations and technical documents concerning topics related to the study of UFO events. These reports were made publicly available. These reports are no longer being disseminated, but some information can still be requested from CNES.


    Appendix 2: Procedures for Analysis of Photographic Evidence


    The Panel recommends that, given a new alleged UFO photograph, the decision to invest effort into its investigation should be taken only if both of the following conditions are fulfilled:

    1. the original documentation (negative, slide, videotape) is available, and
    2. there is at least one other independent source of information – either witness testimony or some other physical record.

    If, after visual examination, the displayed object has not been identified (planet, balloon, cloud, etc.), investigation should be performed in two steps:

    Step 1 consists of establishing or rejecting the authenticity of the photograph (or other record), taking into account evidence for unintentional false operation of equipment and various spurious phenomena that may affect the recording equipment. However, this concept of authenticity is at best relative, since in this area of investigation only negative conclusions may be considered as final, so that authenticity can never be demonstrated absolutely.

    Step 2, if warranted, consists of extracting as much information as possible from the photograph or other record, so as to obtain as much information as possible about the object of interest (size, shape, distance, albedo, emitted energy, spectrum, etc.).

    When the original film is available and analysis seems justified, all technical data concerning the site, viewing conditions, camera, film, processing, etc., must be collected. If the camera is available (in an ideal case still loaded with the original film), it must be used to perform the following calibrations:

    1. Photos of density patterns for relative photometry;
    2. Photos of sources calibrated in intensity, in various positions in the frame (for absolute photometry);
    3. Photos of spatial frequency patterns, to determine the modulation transfer function (MTF); and
    4. Photos taken at the same site as the original, eventually with models to simulate the object.

    The film should be processed under rigorously controlled conditions (if it has not already been processed commercially). If the camera is available but empty, the same operations should be conducted with a film of the same type as the original.

    The investigator should visit the original site and make measurements concerning the three-dimensional geometry of the observed landscape or this information should be extracted from detailed maps. If the photograph has been acquired at nighttime, an astronomical map of the sky at the time of acquisition will be necessary. The investigator should determine the meteorological conditions from the official offices or air bases in the neighborhood with particular attention to the horizontal visibility. The investigator should also take into account all quantified or quantifiable elements of the witness testimony including the estimated shape, angular size, velocity, color, etc.

    For analysis of the photograph, it is essential to work from the original negative. This should be carefully washed and examined under a microscope to look for possible tell-tale artifacts and scratches, and to check the regularity of the grain structure so as to detect multiple exposures. The negative should be analyzed by conventional photographic instruments (enlarger, projector, etc.), and the information on the negative should be digitized by a microdensitometer.

    Once digitized, the image may be analyzed by computer analysis, using the classical tools of contrast enhancement, noise suppression, contour detection, restoration, etc., and more specialized techniques such as maximum-entropy analysis that may be used to remove the effects of target motion and/or camera motion. Such analysis will assist in the detection of a possible hoax. For instance, a suspension thread may be brought into evidence through standard differential operations. Also, one may estimate the distance (hence the size) of the object through MTF computations, based on an analysis of atmospheric diffusion and contour blurring. If there are black areas on the object, it is possible to obtain estimates of the distance by comparing the luminance of such regions with other identified black parts of the scenery. If the object is nearer than the minimum depth of field, one should be able to detect geometrical distortions in the image. If the operator had a slight movement while taking the picture, analysis of the corresponding blur on the object and on other elements of the landscape may allow the calculation of a possible range for the distance of the object.

    In the case of a color photograph, one should carry out the above procedures in three steps using three appropriate color filters for scanning.

    If an event is recorded on a cine camera, each frame may be analyzed as above. However, it is now possible to obtain additional information by combining and comparing the sequence of images.

    In principle, images recorded by video cameras may be subjected to comparable analyses. However, video records suffer from one very important weakness: since the basic data is in electronic form, it could have been modified by the use of suitable electronic equipment, so that the authenticity of a video record will depend even more critically upon the credibility of the witness testimony.


    Appendix 3: Formation Flying


    A recurrent theme in certain UFO reports is the concept of an apparition that flies in formation with an aircraft-borne observer. Without making a judgment on any such reports, we could recommend that UFO investigators familiarize themselves with natural phenomena that display this “flying-in-formation” characteristic. Greenler (1980) is a useful resource, from which the attached list was made. The precise mechanisms for the origin of most of these phenomena have been determined and are explained in Greenler, but quite a few have still not been deciphered satisfactorily. Even an experienced observer might be surprised in seeing a particularly rare example. I have studied certain related phenomena in my research involving electromagnetic probing of planetary atmospheres, but was quite astonished a few years ago when I saw a particular example of the following list. A bright white light flew for minutes in perfect formation between my aircraft and the ground, with the air below and above apparently being transparently clear.

    Formation flying phenomena:

    Arcs: Kern, Lowitz, Wegener anthelic, Hastings anthelic, Tricken anthelic, Parry, alternate Parry, suncave Parry, sunvex Parry, upper tangent, lower tangent, supralateral, infralateral, circumzenithal, circumhorizontal, anthelic, subanthelic, contact.

    Halos: Hevel, 8 degree, 18 degree, 22 degree, 46 degree, circumscribed.

    Bows: fog, cloud, dew, supernumerary.

    Rainbows: primary and secondary; direct and reflected; raindrop and ice crystal; white, red, and red-to-blue.

    Pillars: sun, moon, city-light, anthelic.

    Rings or Circles: Bishop, Bottlinger, parhelic, subparhelic, coronal.

    Dogs: sun, moon, elongated, subsun.

    One should also consider: Nighttime: moon, Venus, Jupiter, bright stars, etc., gegenschein, zodiacal light, comet, in-cabin light reflected by window.

    Other forms: glory (specter of the Brocken), subsun, wet and dry heiligenschein, seven suns, lenticular and other distant small clouds, several different kinds of mirages.

    The phenomenon which was a special surprise to me is one in the final grouping, the subsun, due to particularly stably falling, flat, horizontal, hexagonal, ice crystals which were sufficiently few in number that the air appeared clear in every direction except the solar specular direction to the side of and below the airplane, where they efficiently mirrored the sun.


    Appendix 4: Electromagnetic-Wave Ducting


    It is possible that some of the radar cases presented to the panel have a natural explanation. It seems likely that some possible natural explanations could be investigated without cooperation or assistance from the controlling military authorities except for a time record of unidentified traces that occur during designated test periods.

    Some of the observations suggest that time-variable atmospheric ducting may on occasion result in echoes being obtained from distant ground locations as a result of refraction. Some of accounts described (a) groups or swarms of echoes that persist for some time in the same general location; (b) apparent trajectories of echo sources that exhibit sudden changes in the vertical and/or horizontal positions; and in particular (c) the tendency of apparent echo sources to concentrate over mountain tops. These are all characteristics to be expected of ducting conditions due to weather. These effects can come and go over long periods of time and they can also lead to scintillation or other changes over short time periods. (See, for instance, Hall & Barklay 1989.)

    An atmosphere is said to be “superrefractive” when a horizontal light or radio ray curves downward with a radius of curvature that is less than the distance to the center of the planet. The atmosphere of the planet Venus is at all times globally superrefractive below an altitude of about 30 kilometers. In principle, echoes could be obtained from every area of the spherical surface of Venus from a radar system located at any position on the surface. If the air of Venus were perfectly clear, an observer would see all areas of the surface, all areas repeating in range to indefinite distances. In the four giant planets also, the large gradients of refractivity (or density) in their atmospheres produce superrefractive conditions.

    The Earth’s atmosphere is normally not superrefractive. However, common weather effects (in particular thermal inversions, where the air temperature increases with altitude, and/or the water-vapor content decreases with altitude) can and do produce regions of superrefraction that are localized geographically and in height. As a result, atmospheric ducts (channels that trap and conduct radar waves) can form that carry the signals far beyond the normal horizon. Such ducts can bend rays down to a distant surface area or, more easily, to a distant mountain top. Backscattering of the radar energy from the ground or from discrete objects on the ground then results in echoes that appear to the radar to be due to a target that is far away and (if the angle of elevation of the returning energy is measured) high in the atmosphere. A similar transient ducting of sound can produce the experience of hearing the whistle of only one particular train out of the many that originate at difference times from a busy track in the next valley.

    As is well known, atmospheric ducting is the explanation for certain optical mirages, and in particular the arctic illusion called “fata morgana” where distant ocean or surface ice, which is essentially flat, appears to the viewer in the form of vertical columns and spires, or “castles in the air.”

    People often assume that mirages occur only rarely. This may be true of optical mirages, but conditions for radar mirages are more common, due to the role played by water vapor which strongly affects the atmospheric refractivity in relation to radio waves. Since clouds are closely associated with high levels of water vapor, optical mirages due to water vapor are often rendered undetectable by the accompanying opaque cloud. On the other hand, radar propagation is essentially unaffected by the water droplets of the cloud so that changes in water vapor content with altitude are very effective in producing atmospheric ducting and radar mirages.

    With regard to “impossible” flight paths that may appear to be indicated by some of the echoes obtained by military radars, it is important to note that the records presented to the panel are based on measured time delays and measured elevation and azimuth angles-of-arrival of the reflected energy from the echoing object. As presented, certain target positions were plotted as height versus time. But height is computed from two parameters: (1) the measured time delay, which is a very good indication of range; and (2) the measured vertical angle of arrival, which may not be a valid representation of the vertical direction to the target. In particular, when ducting occurs, reflections from distant and distinct surface targets (buildings, bridges, trucks, etc.) may be received at elevation angles of several degrees, so that a ground target at a range of 100 kilometers, for example, would appear to represent an object at a height of several kilometers. Atmospheric turbulence would distort the duct and could cause sudden changes in angle of perhaps a few tenths of a degree, which would be interpreted as a sudden change in altitude of the order of half a kilometer. The horizontal angle of arrival would also be affected by turbulence, adding to the chaotic character of the apparent flight path.

    Ducting to and from distant mountain tops requires less refractive bending than echoes to and from lower surface areas, and should therefore be more common. This may explain the concentration of apparent targets over mountains. A test of this hypothesis would be to place a radio receiver, tuned to the radar frequency, on or near the top of a mountain associated with unidentified targets. It should be connected to an antenna that has its unobstructed receiving lobe centered in the azimuthal direction of the radar and its vertical pattern extending from zero to at least several degrees in elevation. If ducting does in fact occur, the occurrence of unidentified radar echoes would be found to be correlated with major increases in the strengths of the radar signals measured by this receiver.


    Appendix 5: Sprites


    One of the optical displays reported by E. Strand may be of special significance as a tentative bridge across the wide gulf that exists between the UFO and scientific communities.

    Two women reported an unusual, colored, intermittent light display that slowly moved over two hours of observation made from a remote cabin in Norway in the post-midnight hours of August 3, 1991. The sky was clear until the end of the observation period, when a few clouds moved in. The key point about this display is that while there was no local thunderstorm activity, there was an electrical storm in the direction of the display, but the storm was 120 kilometers away. For decades, it has been conventional scientific wisdom that all of the visible electrical activity of such storms is within and below the clouds, that in this case would have been below the observers’ horizon.

    Recent developments in the observations and theory of electrical activity in the high atmosphere (mesosphere and low ionosphere) demonstrate that this conventional wisdom is in error (see, for instance, Pasko et al., 1996; Sentman & Wescott, 1995). Some of the reports of observations in the Hessdalen area could be related to phenomena that occur above storms, up to an altitude of nearly 100 kilometers, well above the observers’ horizon. This electrical activity goes by the names of “blue jets,” ” red sprites,” and “short-lived elves.” There have in fact been sporadic reports of these phenomena decades ago, but these reports were dismissed by the “experts.” Now these events have been captured on film and video.

    This example can serve to remind us of the continual development and change that occurs in all fields of scientific knowledge, and of the potential advantages of open communication between the purported experts and interested amateur observers.


    Appendix 6: SETI and UFO Investigations Compared


    My perception is that the SETI (Search for Extraterrestrial Intelligence) and UFO studies of a decade ago shared positions beyond the pale of “respectable” science. They no doubt still do in the view of many scientists. However there have been several fundamental advances during the past few years that indirectly provide some increase in plausibility for both areas, and the SETI community seems to be responding with renewed vigor. It may be useful for our panel to consider some UFO-SETI comparisons, and the different cultures of their respective participants. These are my personal and incomplete thoughts on this subject.

    There have been recent advances concerning the question of the possible existence and state of extraterrestrial life (ETL). Knowledge that there is such life would increase the presumptive probability of extraterrestrial intelligent life (ETIL). SETI investigators search for the latter mainly by examining the radio spectrum for telltale electromagnetic signals that may be purposely sent or inadvertently leaked from a technological society. UFO investigators may invoke visitation by ETIL as a fallback or default explanation of an apparition or event which they believe cannot be explained any other way. There are huge gaps in our knowledge that must be filled in before we can pretend to understand either of these subjects.

    With regard to the first question, the existence and possible abode of ETL, three major recent developments are of particular note:

    1. It is only in the last few years that we have finally obtained direct evidence of the existence a planetary-sized body orbiting a star other than our Sun. We now have evidence for several (of order of 10), and more are being discovered as the Doppler observational technique is being improved. There are billions of stars in our galaxy alone, and these results suggest that stars may quite generally be accompanied by planets. One may expect that conditions on these planets would vary over a wide range, at least as wide as the range covered by the planets of our solar system. (See, for instance, Cosmovici et al., 1997.)
    2. Life that is fundamentally different from nearly all near-surface life on Earth has been found deep in terrestrial rock and in the deep ocean, where it exists under conditions long assumed to be so hostile as to be sterile. It would appear that near-surface and subterranean life forms are essentially independent and that either could exist without the other. It is also possible that life started several different times on Earth after epochs of total extinction caused by asteroidal and cometary impacts. These new findings suggest that life might have started independently at two levels on Earth, or that life can adapt to extraordinarily different environments. The development of life, under conditions that are thought to be favorable and under conditions that we previously thought to be unfavorable, may be the rule rather than the exception for the innumerable planets that probably exist in our galaxy. (See, for instance, Cosmovici et al., 1997.)
    3. A meteorite found in Antarctica and known to have come from Mars (from isotopic “fingerprinting” of its elements) has several detailed internal characteristics (structural, chemical, and elemental) that may, it is claimed, be attributed to effects of ancient microscopic life indigenous to Mars. (McKay et al.,1996). This interpretation is controversial and research on this and other meteorites is continuing.

    These subjects are currently being investigated widely and were featured among the many areas discussed at an international meeting in July 1996 held in Capri, Italy, on the subject of Astronomical and Biochemical Origins and the Search for Life in the Universe (Cosmovici et al.,1997). About 200 astronomers, biologists, chemists, physicists, and other scientists from 27 countries met for this Fifth International Conference on Bioastronomy and Colloquium No. 161 of the International Astronomical Union. This meeting was supported by international and national scientific organizations including the International Astronomical Union, the International Scientific Radio Union, the National Aeronautical and Space Administration, the European Space Agency, the Consiglio Nazionale delle Richerche, and other Italian organizations; clearly, this was a mainstream scientific meeting. The SETI community was very visibly represented in all aspects of the conference, but the problem posed by UFO reports was never mentioned.

    However, the UFO and SETI communities share defining attributes including a surfeit of putative evidence that remains unidentified, and the lack of a single example that can be unequivocally verified, repeated, understood, or captured. That is, both are subject areas of investigation that totally lack identified objects. Then why is one moving into the mainstream of acceptable science while the other is not?

    It may not be generally realized that the several different groups of SETI observers have received and tabulated an appreciable number of URS, or unidentified radio signals, in the course of listening to billions of radio channels for hundreds of thousands of hours, looking in tens of thousands of directions. They measure signals that are noise and signals that range up to many times stronger than can be explained in terms of natural noise. They identify nearly all of the strong signals as coming from radio and TV stations, from military radars and various kinds of communications systems, from satellites and deep space probes launched by various national and international organizations, and from many kinds of equipment that leak electromagnetic energy over broad spectral bands. After very thoughtful and vigorous winnowing, there has been a residual number of strong signals received by every group that are, and will no doubt remain, unidentified. But these are not described and released to the media as something unusual or mysterious. This is because they could not be verified by other observers or by repeat observations at the same frequency and in the same direction in the sky. Improved techniques and protocols are being developed to markedly reduce the frequency of URS (even to the point where there may be concern that a real ETI signal could be discarded). Nevertheless, it is to be expected that continuing URS will persist in the SETI endeavor, and will remain unidentified and undiscussed.

    The SETI participants include a large fraction of scientifically trained radio astronomers, and they employ complex and expensive equipment that includes the largest antennas and most sensitive electronic and digital systems in the world. The UFO community is much broader and diverse, and cannot bring to bear the instrumental firepower that is routine in SETI research. In fact, no equipment is involved in most UFO case studies. The nature of UFO phenomena is such that it would be unreasonable to demand repeat observations of the same kind of incident and independent confirmation of events by different observers.

    However, the status of UFO studies may be improved if we can find a way to move in a direction where independent confirmation and repeatability could be realized and become routine. Where some level of repeatability exists but explanations are incomplete (e.g., in the Hessdalen project), more investigative resources are clearly required. Open channels of communication between UFO investigators and a broader scientific group may lead to natural explanations of many observations and thereby winnow the numerous reports to a few notable examples to which intense cooperative efforts could be applied.


    Appendix 7: Further Thoughts on SETI and UFO Investigations


    The SETI and UFO problems may or may not be related to each other. As there does not so far exist any proof concerning this question, it seems wise to keep those two problems apart and not to confuse them. The questions raised by the UFO and SETI problems are not at all comparable, and the strategies for their research are drastically different. The SETI problem corresponds to a one-bit theoretical question: does there exist, elsewhere in the universe, any form of intelligence that has reached the technological level of transmitting intelligent electromagnetic signals that humans could detect and identify? Although this question is undoubtedly exciting and justified by existing probabilistic computations about the existence of planets, the appearance of life, the duration of a civilization, etc., the final answer is theoretically Yes or No. However, only a Yes answer will be final, since a No answer may be revised in view of technical improvements of detection techniques.

    The UFO problem arises from the verified existence of a very large and coherent set of testimonies worldwide. Its approach is bound to be in three steps:

    Step 1. Try by all means to identify the stimulus that has led to the report: the report may be due to inadequate information, misinterpretation of a familiar phenomenon or device, an unusual astronomical or atmospheric phenomenon, an unusual technological device, or a hoax (perpetrated by the reporter or on the reporter).

    Step 2. If Step 1 has not yielded an explanation of the report, try to characterize the event that led to the report and compare it with other case descriptions.

    Step 3. For any case that is strong in testimony and rich in detail, one should try to define a model. In this activity, we are clearly not dealing with a simple question with a Yes /No (one-bit) answer. Different cases require analyses with different levels of complexity.

    The SETI and UFO problems also involve different approaches. Scientists may pursue the SETI project and remain in a very familiar environment: the relevant technological area is clearly identified and one may follow a predefined strategy by specifying the frequency search band, the required receiver sensitivity, the intrinsic properties of an intelligent signal, etc. On the other hand, research on the UFO problem is necessarily complex, multidisciplinary, unpredictable and must be expected to evolve as research progresses. The basic detection is usually carried out by unprepared human beings, and analysis may call upon a wide range of disciplines including human perception, psychology, astronomy, image processing, physics, chemistry, etc. Moreover, effective research in this field must be conducted with an open mind.

    Although in public opinion the UFO and SETI projects are closely associated, they should be kept clearly separated as far as serious research is concerned. The questions being addressed are quite different in nature: the SETI project aims at a simple Yes/No answer to the question of the existence of extraterrestrial intelligence, whereas research into the UFO project must be pursued with a completely open mind as to the questions that need to be posed and answered. Moreover, the respective technical strategies have nothing in common: SETI research is carried out primarily within the established framework of radio astronomy, whereas UFO research is necessarily multidisciplinary and innovative.


    Appendix 8: Scientific Inference


    In attempting to resolve a complex problem such as that posed by UFO reports, one is very much in the “gray area” of scientific research that is not well defined: the facts are to some extent shaky; some of the hypotheses are speculative; and it is not clear how to evaluate the hypotheses on the basis of the facts and of other relevant information. Furthermore, one has the difficulty of relating the analysis of individual reports (“Is this report due to a hoax?”) to the global questions represented by the hypotheses (“Are some reports due to hoaxes?”). In such a situation, it is essential to have some way to organize one’s analysis of whatever research is being conducted. Scientific inference is the intellectual basis of science, and the procedures of scientific inference offer a framework for organizing such analyses. (See, for instance, Good, 1950; Jeffreys, 1973.)

    The formalism of scientific inference involves expressing all judgments in terms of probabilities. Where there are definite rules for deriving probabilities from the evidence, these rules can be used; otherwise, the probabilities may be regarded as subjective. If each judgment is made by several investigators, this can provide both a mean or consensus estimate and a measure of the degree of uncertainty of that estimate. For a recent exposition of this formalism, see for instance Sturrock (1994d)

    In investigating any specific case, it is necessary to work with a complete and mutually exclusive set of hypotheses. The following set of 8 hypotheses was used in Sturrock’s survey of the members of the American Astronomical Society (Sturrock, 1994a; 1994b; 1994c):

    a. Hoax,
    b. Some well established phenomenon or device,
    c. Some well established but unfamiliar natural phenomenon,
    d. Some unfamiliar terrestrial technological device,
    e. Some hitherto unknown natural phenomenon,
    f. A technological device not of terrestrial origin,
    g. Some other cause which [the investigator] can specify, and
    h. Some other cause which [the investigator] cannot specify. An investigator may begin by assigning “prior probabilities” to these hypotheses, although this is not essential. If so, each value must be greater than zero and less than unity, and they must sum to unity. Once these prior probabilities have been assigned, the investigator should then forget about his prejudices.

    Bayes’ theorem then provides a mechanism for updating one’s assessment of probabilities on the basis of new evidence. The new evidence may be a single case or an analysis of a catalog of cases. When measurements are made in terms of “log-odds” defined by log[(p/(1 – p)] rather than the probability pitself, it turns out that investigators with very different prejudices should assign the same weight of evidence, measured by the change in log-odds, to the same experimental or observational data. Hence, although they may differ in their prejudices, they should be able to agree in their assessments of the evidence.

    It is even more convenient to work in terms of the quantity 10*log[p/(1-p)], since one may then use the familiar engineering term “db” or “decibel” to represent an assessment. For instance, if one begins with the assessment that the probability of an event being due to an extraterrestrial vehicle is 10-6, one could rephrase that as saying “my assessment is -60 db.” If a certain research program made that proposition even more unlikely by, say, 10 db, one would then lower that assessment to -70 db. If, on the other hand, the evidence seemed to support that hypothesis with weight 10 db, the resulting assessment would be -50 db. If six separate and completely independent studies were each to yield evidence of 10 db, the investigator would end up with an assessment of 0 db, which represents even odds of the proposition being true. That is, the evidence would have been just sufficient to change the mind of the investigator from being highly skeptical about the hypothesis to considering it just as likely to be true as not true.

    It is highly unlikely that any research project that is in operation for only one or two years will solve the UFO problem. However, it could and should provide useful relevant evidence, and that evidence should lead to a measurable change in the assessments of an interested scientist. In an area such as that of UFO research, that is all that can be expected. On the other hand, several research projects, each lasting a reasonable length of time, should provide sufficient evidence that an hypothesis may be effectively definitely established or definitely rejected.

    If these suggestions are considered to have merit, they could be developed into a more specific and more useful form by means of a workshop that brings together UFO investigators, professional investigators (of accidents, failures, etc.), physical scientists, and statisticians.

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