Avalanches and Avalanche Receivers


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Comparison Test for Avalanche Beacons

The Swiss Federal Institute for Snow and Avalanche

Provided by Paul Wilson, December 1998

Introduction

After 1990 and 1994, the Swiss Federal Institute for Snow and Avalanche Research (SLF) in Davos organized another international comparison test for avalanche beacons. The test "LVS-98" was carried out under the auspices of the International Commission for Alpine Rescue (ICAR). Financial support was provided by the Swiss Council for Accident Prevention. Various alpine clubs and organizations (from Germany, France, Italy, Austria and Switzerland) participated. The tests were necessary to obtain a clear picture of the quality of the new types of beacons, all of which have mostly digital type optical search aids.

The Purpose

The purpose was to clarify the state of the art applied, to enable users to assess the quality of the equipment available on the market, and to show the manufacturers the strengths and weaknesses of their products.

Equipment tested

The tests covered five of each avalanche beacons from six manufacturers. Three of those units were newly developed and equipped with optical search aids and mostly digital technology: Arva 9000 (France), Ortovox M1 (Germany) and Tracker DTS (USA). The Ortovox M1 units came only from a pre-production series. The other three units were of the conventional type and were also used as reference units to the comparison tests conducted in 1994: Barryvox VS 2000(Switzerland), Fitre Snow Bip II (Italy) and Pieps 457 Opti 4 (Austria).

Test Program

The field tests were carried out on 17 days in September and October 1998. Well over 1000range tests and over 400 locating tests were performed on Les Diablerets(Glacier de Tsanfleuron, Switzerland), on the Stilfserjoch (Italy), in Allevard (France) and on the Stubaiglacier (Austria). It was possible to run the tests on snow at three out of the four locations. It was essential to ensure uniformity of the test conditions as far as possible and, with this in mind, detailed test instructions were produced and a three-man SLF test team was assigned to attend the tests. Immediately after the tests, those involved in the tests were asked to complete a detailedquestionnaire dealing with such matters as operating safety, operation, locating system, carrying system and operating instructions. The equipment was finally measured electronically at an approved test laboratory and the main properties of the units checked to ensure compliance with European Telecommunication Standards (ETS 300 718).

Field Test Results

Effective range

The results of the field tests showed that the average ranges of the new type units (20-30 m) are in some cases much shorter than those of the proven reference equipment that have ranges between 30 and 45 m. This gives relatively small search strip widths from 18 to 21 m. The search strip width is statistically defined so that a person buried in an avalanche would be missed by the search no more than twice out of 100.

Search Times

In the case of the locating tests, only the time needed for the secondary search, that is from the first signal up to the precise location, was measured. The transmitters were buried 1 m deep. Of all the three new type units, Tracker DTS came out best in search times, followed by Ortovox M1. On the average, these two units produced shorter search times (in the case of approx. 30 tests each) than with the two reference units Barryvox VS 2000 and Pieps 457 Opti 4. These results would even be a little better if the reference equipment used was handled by people who were less well familiar with it.

Locating Accuracy

In the tests on locating accuracy the transmitter units were again buried 1m deep. The proven equipment turned out to be better as regards locating accuracy but the differences are rather small. The mean values (median) are between 34 cm from the best unit (Barryvox VS 2000) and 70 cm from the worst unit (Arva 9000). The scatter varies between units and is partly quite large. The proportion of cases where the locating error was smaller than 80 cm, was in the case of Arva 9000 57%, in the case of Tracker DTS 67% and in the case of Ortovox M1 71%. Generally speaking, units with analog acoustics came out somewhat better. Arva 9000 has a very wide scatter, reflected as well in the tests on range and search time, clearly indicative of some problems with delayed display of the receiving signal.

Locating Tests with two Transmitters

Searching for multiple burials produced some critical results. The two transmitters were buried 5 m from each other, one 0.5 m deep and the other 1 m deep. Arva 9000 failed to identify the presence of the second transmitter in as many as 15 cases out of a total of 17. Five searchers were unable to locate the second transmitter even when its presence was indicated. When using Tracker DTS, 11 out of 23 testers did in fact identify two victims buried near to each other but the location of the second transmitter could not be identified again in 5 cases in spite of its presence having been indicated. The Ortovox M1 came out best of the three newly developed units: 13 out of 15 testers identified the presence of two transmitters; and the second transmitter could not be located, in spite of its presence being indicated, in only one case. All the testers taking part were very experienced. Even if it is assumed that when members of the own party are searched for, the number of buried victims is known in many cases, this result is still very disappointing. Only some results were available for the proven equipment. Using a Pieps 457 Opti 4 the second transmitter in 3 out of 8 cases could not be located but was found when its presence was indicated. No problems occurred in the remaining only 5 tests with Barryvox VS 2000 and Fitre Snow Bip II.

Further Observations

The equipment was repeatedly wrongly manipulated throughout the 400 locating tests. In 3% of the tests, testers tried to start searching with a unit in a state of operation with which it would have been impossible to find a buried victim. This percentage is quite high if we consider that these testers were in fact trained people and that these were staged search exercises. It is possible to figure out easily what the situation would be in the case of a real avalanche accident when searchers work under considerable stress. The display showing the searcher the operation mode is insufficiently clear on some of the beacons tested.

The automatic switch-over to "transmit" on Tracker DTS and Barryvox VS 2000 is still controversial and was not liked by most of the testers.

Tests carried out during one day with 12 to 14 year old schoolgirls and boys have not been conclusive. The number of tests was too small. The three new units and the Pieps 457 Opti 4 have been tested. The search times did not reveal really clear differences between units. The scatter is very large. However, Tracker DTS showed the smallest locating error. For these tests the transmitters were only buried 30-50 cm deep.

Rescue Time

Close interrelation of search strip width, locating time and overall rescue time can be calculated from two concrete examples of an avalanche deposit, a small one 30 m wide and 40 m long, and a medium sized 50 m wide and 80 m long. In fact, greater range means a short primary search but a longer secondary search, and vice versa. In the case of a short range unit, the search is very quick with such a unit on a small avalanche deposit but it takes quite a bit more time on a large avalanche. A beacon with a relatively long range compared with a short range unit takes only slightly more time on a small avalanche but such a unit works much faster on a real large avalanche.

Summary of the Field Test Results

The following table gives a summary of the test results. Table 1: Summary of the field test results. The average search time(secondary search) is the time from the first signal up to precise location and represents only one part of the total rescue time. The times are not representative of a search on an avalanche deposit. The search in a serious case lasts much longer. The mean location error (median value) refers to a burial depth of 1 m.

Receiver Mean Range Strip Search Width Mean Search Time Mean Location Error
Arva 9000 28 m18 m3:14 min70 cm
Ortovox M1 30 m21 m2:22 min48 cm
Tracker DTS 20 m20 m2:04 min50 cm
Barryvox VS 200045 m50 m3:09 min34 cm
Pieps Opti 4 31 m29 m2.54 min54 cm

Results of Laboratory Measurements

The 457 kHz frequency is maintained within the standard tolerance in the case of all units. The accuracy of the transmitter frequency of the two reference units Barryvox VS 2000 (+2 Hz) and Pieps 457 Opti 4 (+/- 0 Hz) is excellent. Greater deviations, no doubt having a negative effect on compatibility, but still remaining within the standard tolerance of +/- 100 Hz, were found in Tracker DTS (+60 Hz) and Ortovox M1 (-49 Hz). In the case of Ortovox M1, the transmitting frequency of three out of the five tested units (from pre-series production) even dropped slightly below the tolerance limit at low temperatures.

In the case of all the tested beacon equipment, the strength of the transmitting field is close to the maximum permissible standard value. This results in an encouragingly long transmitting range for all the units. This reach is reduced only marginally at low temperatures (-20C). On the other hand, the effect of the battery condition is slightly greater than that of the temperature.

Figures equivalent to a 10% reduction in range were found by measurement. Battery life in the "transmit" operating mode was around 300 hours in most units, varying from 180 hours (Tracker DTS) up to 700 hours (Barryvox VS 2000).

Testing receiver sensitivity the greatest differences were found not only between the units from various manufacturers but also within the same make. While the results of laboratory measurements carried out on Arva 9000 and Barryvox VS 2000 were clearly satisfactory, receiver sensitivity figures found by the test laboratory for Pieps 457 Opti 4 and Ortovox M1 compared with the ETS standard were inadequate by a narrow margin. Receiver sensitivity values in the case of Tracker DTS, measured by an accredited electronics laboratory, were found to be far too low.

Evaluation of the Questionnaires

After the practical tests, the units were assessed (subjectively) by all testers on the basis of a questionnaire containing 40 questions. These questions are arranged in the following 5 main groups: operating safety, operation, locating system, carrying system, operating instructions and miscellaneous. Evaluation of the new type units is based on the answers from 52 questionnaires each. Far fewer questionnaires are available for the reference units; there are 11 for Barryvox VS 2000, 15 for Fitr Snow Bip II and 21 for Pieps 457 Opti 4. The 5-grade scale ranges from very bad (grade 1) up to very good (grade 5). Ortovox M1 comes out as the best among the three new type units. Its grades for the three essential features (operating safety, operation and locating system) are practically as good as those for the reference unit Pieps 457 Opti 4.

Good grades for the locating system of Ortovox M1 are due to the assessment given to the proven acoustic part; on the other hand, the optical search aid is described in many comments as unsatisfactory. Tracker DTS, its handling in particular having been given lower grades, is second best from among the new type equipment. The Arva 9000 with its locating system having also been given an unsatisfactory average mark, is clearly the worst.

From a total of 50 questions, Barryvox VS 2000 is described as unsatisfactory on only two points; Pieps 457 Opti 4 and the new Ortovox M1 have 3 unsatisfactory points, Fitre Snow Bip II 6 points and Tracker DTS 8 and Arva 9000 22 points with an unsatisfactory average grade. So the well-proven reference equipment is not free from imperfections as well. For example, the testers' opinion of Barryvox VS 2000 was negative as regards its size, weight and price, and the automatic switch-over.

Conclusions

The overall picture (field tests, laboratory tests, questionnaires) reveals Ortovox M1 as the best of the three newly developed units tested, followed by Tracker DTS, and with Arva 9000, with generally the worst grades, trailing at the end.

In spite of the fact that advanced features have been introduced to user controls in all three units (optical search aids based on a digital system) and, in the case of Ortovox M1 and Tracker DTS, the search time has also been improved, all three units still have some imperfections. They affect particularly the search for multiple burials (Arva 9000, to some extent Tracker DTS), the locating system (Arva 9000, to some extent Ortovox M1: optical section) and the handling (all three). In addition, for all three new beacons the search strip width is small. Accordingly IKAR's recommendation is very clear and based on the principle that vital safety equipment should not have any serious imperfections.

There is no doubt that the newly developed equipment is heading in the right direction. The new optical displays offer advantages but are frequently too extensive and in the case of Ortovox M1 even rather confusing. Features of promising solutions have been found in the locating system (Tracker DTS: two receiving antennas, best direction indicator) or in the combination of analog and digital technology (Ortovox M1). In simple situations (small avalanche, only one buried victim, shallow depth etc.), untrained persons should achieve rather better results with Tracker DTS or Ortovox M1 than with the proven equipment. The disappearance of sensitivity regulators in some cases should also be regarded as welcome. Therefore, it is to be hoped that the manufacturers will not be discouraged by the test results and that they will eliminate the imperfections soon. The true dynamism displayed by the development of the beacon equipment will no doubt lead to substantial improvements for the benefit of the user. It appears to be quite possible that further development will bring us in the near future a big step closer to the target which is easy-to-control, efficient and reliable avalanche rescue search equipment.