Am Bodach, Stob Ban, Sgurr an Iubhair and Mullach Nan Coirean

Pedantic Surveys

Survey report C725

Am Bodach, Stob Ban, Sgurr an Iubhair and Mullach nan Coirean

25 July 2014

Survey location: Mamores Reference grid square: NN1365 Surveyor: Alan Dawson Report completed: March 2017 Contact: [email protected]

Survey equipment GNSS controller: Leica RX1250X GNSS antenna: Leica ATX1230 Antenna support: Draper tripod and one-metre survey pole Levelling: Leica Disto D510 laser level

Survey points and conditions Hills surveyed: 7 Summit survey points: 8 Col survey points: 7 Conditions: Dry, clear, warm, wind light to variable, occasionally strong

Objectives There were several objectives for the day: 1. To measure the relative height of Am Bodach. This was estimated at 151m from OS mapping. 2. To measure the height of Stob Ban, shown as 999m on OS mapping. 3. To measure the height of Sgurr an Iubhair, shown as 1001m on OS mapping. 4. To measure the height of Mullach nan Coirean South Top, shown as 917m on OS mapping. 5. To measure the height of Mullach nan Coirean East Top. This had a 910m contour ring but no spot height. 6. To measure the height of Meall a' Chaorainn, shown as 910m on OS mapping. 7. To measure the height of Mullach nan Coirean, shown as 939m on OS mapping. 8. To measure the height of all relevant cols if possible, to find out the relative height of all seven hills.

Context On a good day, the Mamores offer some of the finest hillwalking to be found anywhere in Scotland. Some people attempt to walk along the whole range in one day, but most walkers opt for a few summits at a time. There are two common approaches to the Mamores – from Kinlochleven to the south or from Glen Nevis to the north. Both of these starting points offer a choice of paths and routes up to the high ground, so there are numerous possibilities and combinations available. The weather in the summer of 2014 was the best in Scotland for many years. The day chosen for the survey was fine and settled, as it needed to be for an ambitious plan to survey seven high summits and seven cols, a total of fourteen survey points. Route The walk began at sea level at Kinlochleven and followed the West Highland Way westward for over 6km to the ruin at Lairigmor. From there, steep but easy slopes led steadily up to Meall a' Chaorainn, the first hill of the day. From there the line of the ridge was followed all the way to Am Bodach, the final hill of the day, with a descent from the col between Am Bodach and Sgurr an Iubhair leading to a path back to Kinlochleven. Sgurr a' Mhaim lies on a subsidiary ridge to the north and was not included in the walk.

1 Owing to the time taken to drive to Kinlochleven, walk 10km and climb over 900 metres, it was after 2pm by the time the first survey point was reached. This was an important factor in determining the amount of data that could be collected at each survey point. The aim was to collect sufficient data to obtain valid results at each survey point, while allocating more time to summits than cols, as the main objectives of the day were to measure the height of all summits, along with the critical col for Am Bodach. Commentary The summit of Meall a' Chaorainn was marked by a large pile of rocks and boulders with little structure, so it looked more like a pile of stones than a cairn or shelter. It was not feasible to remove these rocks in the limited time available, so the first survey point was set up next to the highest visible embedded rock. This look likely to be the natural summit but it was not possible to be certain that there was no higher natural rock beneath the loose pile of rock, so the margin for error was judged to be 0.15m.

The unruly cairn on top of Meall a' Chaorainn, looking toward the reddish top of Mullach nan Coirean The second summit, Mullach nan Coirean , presented a much bigger problem. This hill is quite different in appearance from those further east. Its summit has a mass of loose red granite rocks, with none of the grey quartzite that caps the higher peaks of the Mamores. Thousands of these rocks have been piled up into a monstrous cairn on the summit, making it impossible to locate the highest natural rock without spending a day or more dismantling the cairn. In such cases the best that can be done is to locate the highest visible firm embedded rock and take that as the survey point, while accepting that higher ground might exist beneath the cairn. Even with the tripod extended as far as possible, the antenna was below the top of the cairn, but the satellite numbers and data quality recorded on the GPS controller were reasonably good, so there appeared to be little signal interference from the cairn. It was theoretically possible for a natural rock over a metre high to be hidden inside the cairn but this was judged highly unlikely, so the margin for error was estimated at 0.25m. While data collection was under way, two walkers arrived at the summit from Glen Nevis and began to photograph the superb surroundings. They turned out to be the only two people encountered on the entire walk. The cairn on the third summit, Mullach nan Coirean South Top , was much smaller and less obstrusive, though of no aesthetic merit, so it was easier to locate the highest natural ground next to the cairn. There was less margin for error at the cols on the Mamores ridge than at most of the summits, as most of the cols were narrow and well-defined, with the critical point on the path or short grass next to it. The height of some summit cairns was much more of an impediment to accurate results than the depth of vegetation at the cols. However, the summits did provide better viewpoints.

Unsatisfactory surveying on the summit of Mullach nan Coirean

Mullach nan Coirean East Top was of particular interest as this hill has no spot height shown on any scale of OS map, but it does have a long narrow 910m contour ring, indicating that its height is over 910 metres and therefore could be anything between 910 and 920 metres.

Large-scale OS map of Mullach nan Coirean East Top

If the height turned out to be over 914.4m then this hill would be a new 3000ft summit. As this was considered to be reasonably probable, a longer survey time was given to the summit of Mullach nan Coirean East Top than to other summits. Although this was unlikely to be scientifically necessary in order to obtain a conclusive result, it was judged to be politically necessary, as some authorities were known to be sceptical of results from shorter data collection times, irrespective of the evidence of data quality provided by the GNSS survey data.

Mullach nan Coirean East Top, with Sgurr a' Mhaim (left) and Stob Ban beyond

The path along the ridge of the Mamores passes several metres below the summit of Mullach nan Coirean East Top, as the hill has never been included in the hill lists that are popular with walkers in Scotland. The summit therefore has no cairn. The summit area has several large smooth granite boulders, with the highest one about a metre high and quite obvious. The top of the boulder was too small to provide a stable paltform for the tripod, so the antenna was set up on the survey pole at the side of the boulder. This meant that the base of antenna was slightly lower than the summit, although the top of the antenna was slightly higher, so there was no interference with satellite signals. The height of the boulder above the base of the antenna was measured to be 4cm, so -0.04m was entered into the controller as the height of the antenna. Data was recorded for 60 minutes on the summit. In the good weather this was a wonderful location to rest and enjoy the superb panorama, with Ben Nevis prominent across the other side of Glen Nevis.

Approaching the summit of Mullach nan Coirean East Top

Summit survey in progress on Mullach nan Coirean east Top, with Ben Nevis beyond It was evident that few walkers diverted from path to summit, so it was the most unspoiled and enjoyable summit of the walk so far, regardless of the status of the hill. The continuation of the walk along the ridge eastward toward Stob Ban felt almost effortless in the benign weather, a rare example of the perfect combination of warm sun, gentle breeze, excellent path, fabulous views, valuable data, absence of people and more importantly absence of midges. These were the perfect conditions for surveying in the hills. Satellite coverage was variable and time was slipping away too quickly for comfort, but life is never perfect.

Path bypassing the summit of Mullach nan Coirean East Top

5 Data was duly collected at the next col, the one relevant to Mullach nan Coirean, before the path continued toward the next 910m contour ring, though this one was embellished with a 912m spot height. The path bypassed this minor summit too. With commendable restraint and adherence to objectives, this 912m summit was not surveyed, although it was visited en route. The summit of Stob Ban was encumbered with another untidy mess of a cairn, though much smaller than that on Mullach nan Coirean. Some rocks were removed in order to locate the highest natural point, although it was not necessary to dismantle the entire cairn. That would have been desirable on aesthetic grounds, but the practicalities of surveying objectives were given priority over aesthetics.

Stob Ban from the west, with the minor 912m point on the left

Although the ridge to Sgurr a' Mhaim was left for another day, a short diversion in its direction was made in order to survey the col for Sgurr an Iubhair . This was flatter and less precise than the previous cols but still straightforward compared to those for most lower hills. The summit of Sgurr an Iubhair was slightly different in character to previous summits, a flattish rock outcrop with a large loose pile of rocks sprawled over the top. In order to save time, the survey equipment was quickly set up on this outcrop while further investigation was made. Numerous rocks were removed until a slightly higher part of the outcrop was revealed. Data recording was abruptly terminated and the equipment was moved about two metres along to the highest part of the outcrop. Further checking was carried out while this second summit survey was under way, but no higher point was revealed beneath the rocks. The primary objective for the day, the survey of Am Bodach , had been left until last in order to accomodate the other objectives. Light was fading but the weather remained good and so one last climb was made to the top of Am Bodach, which was reached just before 10pm. Thankfully, the summit cairn here was smaller and the highest point easier to identify. The disappearing sun turned the hillsides red then brown then into grey shadows as the final summit survey was completed. However, the all-important col remained. There was just enough light left to locate the col and set up the survey equipment for the fifteenth time. Just before 11pm the job was done and the equipment packed away for the last time, before the eery descent into Coire na h- Eirghe. The path proved elusive in the dark but was located lower down, where it eventually joined the West Highland Way back to Kinlochleven. No photographs were taken at Sgurr an Iubhair or Am Bodach as there was insufficient light.

6 Results summary Am Bodach 1031.8m P 152.8 Number Type Minutes Offset Margin Feature OS GNSS survey Gridref 303 Summit 22 0.70 0.03 Cairn 1032 151 1031.82 152.75 NN 17637 65097 303 Col 20 0.96 0.03 Grass 881 879.07 NN 16907 65222 Stob Ban 999.7m P 237.1 309 Summit 20 0.80 0.05 Cairn 999 234 999.73 237.14 NN 14777 65443 309 Col 15 0.95 0.03 Path 765 762.58 NN 15670 65382 Sgurr an Iubhair 999.7m P 76.8 308 Summit 20 0.76 0.01 Cairn on rock 1001 77 999.73 76.76 NN 16521 65512 308 Alt summit 6 0.76 0.05 Cairn on rock 1001 999.71 NN 16522 65513 308 Col 16 0.90 0.05 Grass 924 922.97 NN 16366 65643 Mullach nan Coirean 939.3m P 92.3 321 Summit 20 0.91 0.25 Cairn 939 93 939.28 92.30 NN 12233 66243 321 Col 15 0.93 0.03 Grass 846 846.98 NN 14313 65846 Mullach nan Coirean South Top 917.5m P 67.5 323 Summit 20 0.74 0.05 Cairn 917 68 917.48 67.49 NN 13125 65472 323 Col 15 0.89 0.03 Grass 849 849.99 NN 12573 65894 Mullach nan Coirean East Top 916.6m P 38.6 324 Summit 60 -0.04 0.01 Rock >910 35 916.61 38.57 NN 13731 65600 324 Col 20 0.94 0.03 Grass 875 878.04 NN 13436 65447 Meall a' Chaorainn 909.6m P 34.9 325 Summit 20 0.16 0.15 Rock 910 37 909.61 34.94 NN 11497 65734 325 Col 20 0.92 0.03 Path 873 874.66 NN 11822 65811

Key: P: Prominence – a commonly used term for the relative height of a hill (also known as drop) Number: Hill number in the Database of British and Irish hills (DOBIH) Type: The type of topographical feature being measured Minutes: Duration of GNSS data collection at the survey point Offset: Height of GNSS antenna phase centre above the selected survey point, measured by metal tape Margin: Estimated possible margin for error on the ground at the survey point Feature: Nature of the ground at the survey point OS: The height and drop shown on current Ordnance Survey online mapping GNSS survey: The height and drop as measured by the GNSS survey (Global Navigation Satellite System) Gridref: Ten-figure Ordnance Survey grid reference, as measured by the GNSS survey Height figures in the above table obtained from GNSS surveying and processing are shown the nearest centimetre, with grid references giving positions to the nearest metre. However, owing to the margin for error inherent in most hill surveys, height figures are usually rounded to the nearest 0.1m. The margin for error at summits is usually in one direction only, as the summit might be a little higher than measured but is unlikely to be lower. At cols the margin for error can usually be in either direction, as the col can be slightly higher or lower than measured, owing to depth of vegetation, peat or snow.

Results analysis and conclusions Spot heights on OS mapping were shown to be highly accurate on all surveyed summits except Sgurr an Iubhair. The main objectives all produced conclusive results. The relative height of Am Bodach was measured to be 152.8m, so it comfortably retained its existing classification as a Marilyn (a hill of any height with 150m drop all round). Both Sgurr Ban and Sgurr an Iubhair were measured to be under 1000m high, though the summit cairn on Stob Ban limited the accuracy of the result. On Sgurr an Iubhair the margin for error was lower than on Stob Ban owing to the rock outcrop on its summit and the effort made to ensure that the highest rock had been located beneath the loose rocks.

7 The most revealing result was that from Mullach nan Coirean East Top. The measured height of 916.6m is consistent with the contour rings on OS mapping but provides the important detail missing from the maps. The imperial equivalent figure is 3007 feet, so there is no doubt that the summit is over 3000 feet high. The relative height of Mullach nan Coirean East Top was measured to be 38.6m, so there can be little doubt that it would have been included in Hugh Munro's list of Scottish hills over 3000 feet high had he known its correct height. However, he would probably not have regarded it as a separate mountain.

Processing software and models GNSS software: Leica Infinity 2.1 Co-ordinate system: OSGB36(15) Transformation type: Classical 3D Ellipsoid: GRS 1980 Projection type: Transverse Mercator Geoid model: OSGM15 CSCS model: OSTN15(GB) Ephemeris: Precise Troposphere model: Saastamoinen Data recording interval: 30 seconds Satellite cut-off angle: 10 degrees for point 1, point 4 and point 11, 15 degrees for all other survey points The Saastamoinen model was used for processing as some GNSS research had found it to be superior to the Hopfield model, though testing had shown that both models produced height figures within 2mm of each other in most cases. Testing had also shown both Saastamoinen and Hopfield models to be more likely to generate optimum solutions (phase fixed type) than the VMF or Computed models, for hill surveys of up to one hour in duration. Precise ephemeris was used rather than broadcast ephemeris, as extensive testing from other GNSS surveys had shown that it sometimes helped to generate more phase fixed solutions and therefore to produce better data quality than broadcast ephemeris for some survey points.

Processing summary

# Point Easting Northing Height Sat VDOP BS SDh End time 1 Meall a' Chaorainn summit 211497.1 765735.2 909.606 6/8 5.3-8.9 7 0.023 14:34:14 2 Meall a' Chaorainn col 211822.7 765811.1 874.662 7 2.6-2.9 5 0.024 14:59:14 3 Mullach nan Coirean summit 212233.3 766243.0 939.283 7 1.8-2.5 5 0.016 15:34:44 4 Mullach nan Coirean South Top col 212572.7 765896.7 849.994 6 1.4-2.5 4 0.030 16:00:14 5 Mullach nan Coirean South Top summit 213125.7 765472.6 917.475 6/7 1.9-2.3 7 0.017 16:36:14 6 Mullach nan Coirean East Top col 213436.6 765448.7 878.035 9 1.4-1.7 7 0.011 17:03:44 7 Mullach nan Coirean East Top summit 213731.3 765600.2 916.612 11 1.2-2.0 7 0.012 18:15:14 8 Mullach nan Coirean col 214313.4 765846.0 846.978 9/10 1.3-2.7 7 0.015 18:43:44 9 Stob Ban summit 214777.2 765443.2 999.727 8/10 1.7-2.9 7 0.017 19:28:44 10 Stob Ban col 215670.6 765382.6 762.583 8/9 2.6-3.1 7 0.016 20:05:44 11 Sgurr an Iubhair col 216366.3 765642.9 922.969 8/10 1.9-2.1 5 0.015 20:43:44 12 Sgurr an Iubhair alt summit 216522.2 765513.6 999.716 6 2.1 4 0.012 21:02:14 13 Sgurr an Iubhair summit 216521.5 765512.3 999.732 7/9 1.7-2.2 7 0.013 21:23:14 14 Am Bodach summit 217637.3 765097.7 1031.820 6 3.4-3.8 7 0.018 22:14:14 15 Am Bodach col 216907.4 765220.6 879.067 7/9 2.3-7.1 7 0.015 22:50:44 Key: #: Survey point in chronological order Height: Precise weighted average generated from processing GNSS data against OS Net base stations Sat: Number of GNSS satellites available at the survey point and at the nearest OS Net base station VDOP: Vertical dilution of precision, measured against nearest base station (lower number means better data quality) BS: Number of OS Net base stations used to produce the weighted average during processing SDh: Standard deviation for height, averaged across all OS Net base stations End time: Time of final GNSS data recording at survey point Pos diff: Difference between averaged position and position measured against a specific base station Height diff: Difference between averaged height and height measured against a specific base station

8 Processing analysis Data quality was variable but satisfactory for all survey points, with all fifteen points producing valid results from four to seven OS Net base stations. Satellite coverage was also variable. At five of the survey points, only six satellites were available at times, which is only one more than the minimum usually required for accurate differential GNSS surveying. The best satellite coverage was on Mullach nan Coirean East Top, where eleven satellites were available for sixty minutes. Standard deviation figures were reasonable but not as good as in some other surveys, with none of the points having SDh of below 0.010. The most likely reason for this was the effect of the wind on the antenna. This was particularly noticeable in the results from point 4, Mullach nan Coirean South Top col, where the SD figures for easting and northing were unusually high at 0.009 and 0.022, indicating that the antenna was probably moving slightly in the wind, which can sometimes be stronger at exposed cols than at summits. For most points the satellite cut-off angle was set to 15 degrees, but for point 4 the final results were generated from processing the data twice, once with a 10-degree cut-off angle and once with 15 degrees. Data quality was optimised by selecting the base stations that produced the best results from the double processing. The same method was used for point 11, Sgurr an Iubhair col. The other survey point with relatively poor data quality was point 12, Sgurr an Iubhair alt summit, which also produced valid results against only four base stations. In this case the reason was not the wind but the short time for data collection. Point 12 was the interim point on the outcrop on top of Sgurr an Iubhair, where data collection was halted as soon as a higher point had been located, so that no time was wasted recording redundant data. Consequently, satellite data was recorded for only six minutes. This is less than the ten minutes usually regarded as a minimum in favourable conditions, but the result is included in this report to illustrate that even a six-minute survey can produce useful results. The data quality was reduced, but the resulting averaged height was within 0.016m of that recorded for the highest point on the outcrop, two metres away. This is consistent with observations on the ground.

Averaged points summary The tables below show further extracts from the GNSS processing reports generated by Leica Infinity software. They show how the final height figures have been derived from a weighted average of measurements from several OS Net base stations, and also convey the quality of the processed data. If the result from a particular base station is too far away from the weighted mean then it is not used in the final calculation. The cut-off figure for this analysis was set to 0.1m. Figures in red below show data that was excluded from the final result, i.e one base station result for point 4 and one for point 12. The summary tables below show easting and northing to one decimal place, i.e. 0.1m. This refers to the survey point, which is not always exactly the same as the highest point of the hill. For example, on Mullach nan Coirean East Top, the survey point was almost one metre east of the top of the summit boulder. Max. Distance between Average and Measurement: Position: 0.100 m Height: 0.100 m Weighted Average: Yes

# Point Easting Northing Height SD Easting SD Northing SD Height 1 Meall a' Chaorainn summit 211497.1 765735.2 909.606 0.008 0.007 0.023

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 14:34:14 0.014 0.036 -0.074 211497.143 765735.240 909.679 FAUG 25/07/2014 14:34:14 0.052 0.059 -0.024 211497.093 765735.160 909.630 INVR 25/07/2014 14:34:14 0.013 0.033 0.034 211497.101 765735.188 909.572 KILN 25/07/2014 14:34:14 0.015 0.029 0.015 211497.098 765735.207 909.591 LCAR 25/07/2014 14:34:14 0.013 0.018 0.066 211497.146 765735.209 909.540 LOCG 25/07/2014 14:34:14 0.014 0.006 -0.085 211497.134 765735.208 909.690 OBAN 25/07/2014 14:34:14 0.015 0.014 0.036 211497.136 765735.197 909.569

# Point Easting Northing Height SD Easting SD Northing SD Height 2 Meall a' Chaorainn col 211822.7 765811.1 874.662 0.005 0.003 0.024

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 14:59:14 0.006 0.004 0.014 211822.753 765811.158 874.648 FAUG 25/07/2014 14:59:14 0.037 0.039 0.007 211822.719 765811.170 874.655 INVR 25/07/2014 14:59:14 0.006 0.008 0.043 211822.749 7658 11.156 874.620 KILN 25/07/2014 14:59:14 0.023 0.017 0.045 211822.759 765811.141 874.617 OBAN 25/07/2014 14:59:14 0.007 0.022 -0.078 211822.776 765811.169 874.740

# Point Easting Northing Height SD Easting SD Northing SD Height 3 Mullach nan Coirean su mmit 212233.3 766243.0 939.283 0.005 0.007 0.016

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 15:34:44 0.005 0.010 -0.018 212233.319 766243.082 939.300 FAUG 25/07/2014 15:34:44 0.003 0.010 0.027 212233.334 766243 .083 939.256 INVR 25/07/2014 15:34:44 0.004 0.012 -0.028 212233.314 766243.084 939.311 LCAR 25/07/2014 15:34:44 0.006 0.026 0.048 212233.321 766243.114 939.234 LOCG 25/07/2014 15:34:44 0.008 0.041 -0.064 212233.347 766243.124 939.347

# Point Easting Northing Height SD Easting SD Northing SD Height 4 Mullach nan Coirean South Top col 212572.7 765896.7 849.994 0.009 0.022 0.030

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 16:00:14 0.008 0.012 0.005 212572.703 765896.759 849.989 KILN 25/07/2014 16:00:14 0.263 0.187 0.128 212572.892 765896.789 849.866 LCAR 25/07/2014 16:00:14 0.010 0.010 0.067 212572.719 765896.747 849.927 LOCG 25/07/2014 16:00:14 0.014 0.093 -0.026 212572.670 765896.663 850.020 OBAN 25/07/201 4 16:00:14 0.012 0.048 -0.083 212572.731 765896.791 850.076

# Point Easting Northing Height SD Easting SD Northing SD Height 5 Mullach nan Coirean South Top summit 213125.7 765472.6 917.475 0.004 0.003 0.017

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 16:36:14 0.004 0.002 -0.005 213125.751 765472.641 917.480 FAUG 25/07/2014 16:36:14 0.004 0.015 0.020 213125.750 765472.658 917.455 INVR 25/07/2014 16:36:14 0.004 0.018 -0.037 213125.735 765472.631 917.511 KILN 25/07/2014 16:36:14 0.005 0.015 -0.017 213125.734 765472.644 917.491 LCAR 25/07/2014 16:36:14 0.003 0.011 0.058 213125.760 765472.641 917.416 LOCG 25/07/2014 16:36:14 0.004 0.006 -0.056 213125.753 765472.638 917.530 OBAN 25/07/2014 16:36:14 0.010 0.025 0.045 213125.773 765472.651 917.429

# Point Easting Northing Height SD Easting SD Northing SD Height 6 Mullach nan Coirean East Top col 213436.6 765448.7 878.035 0.003 0.004 0.011

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 17:03:44 0.003 0.006 -0.020 213436.688 765448.711 878.054 FAUG 25/07/2014 17:03:44 0.002 0.008 0.021 213436.685 765448.725 878.013 INVR 25/07/2014 17:03:44 0.004 0.014 -0.041 213436.675 765448.711 878.076 KILN 25/07/2014 17:03:44 0.004 0. 018 -0.026 213436.668 765448.715 878.061

10 LCAR 25/07/2014 17:03:44 0.002 0.009 0.026 213436.693 765448.712 878.008 LOCG 25/07/2014 17:03:44 0.005 0.024 -0.044 213436.683 765448.741 878.079 OBAN 25/07/2014 17:03:44 0.005 0.031 -0.013 213436.706 765448.741 878.048

# Point Easting Northing Height SD Easting SD Northing SD Height 7 Mullach nan Coirean East Top summit 213731.3 765600.2 916.612 0.005 0.004 0.012

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 18:15:14 0.002 0.005 -0.026 213731.361 765600.245 916.638 FAUG 25/07/2014 18:15:14 0.003 0.020 0.079 213731.346 765600.264 916.533 INVR 25/07/2014 18:15:14 0.002 0.017 -0.014 213731.348 765600.236 916.626 KILN 25/07/2014 18:15:14 0.003 0.023 0.022 213731.338 765600.241 916.590 LCAR 25/07/2014 18:15:14 0.001 0.011 0.024 213731.370 765600.249 916.588 LOCG 25/07/2014 18:15:14 0.002 0.014 -0.030 213731.354 765600.263 916.642 OBAN 25/07/2014 18:15:14 0.002 0.023 -0.036 213731.373 765600.266 916.648

# Point Easting Northing Height SD Easting SD Northing SD Height 8 Mullach nan Coirean col 214313.4 765846.0 846.978 0.005 0.002 0.015

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 18:43:44 0.004 0.008 -0.056 214313.468 765846.075 847.034 FAUG 25/07/2014 18:43:44 0.002 0.009 0.043 214313.452 765846.079 846.935 INVR 25/07/2014 18:43:44 0.003 0.007 -0.006 214313.454 765846.071 846.984 KILN 25/07/2014 18:43:44 0.003 0.019 0.020 214313.442 765846.070 846.958 LCAR 25/07/2014 18:43:44 0.004 0.019 0.008 214313.478 765846.067 846.970 LOCG 25/07/2014 18:43:44 0.004 0.016 -0.056 214313.477 765846.074 847.034 OBAN 25/07/2014 18:43:44 0.005 0.020 -0.049 214313.477 765846.085 847.027

# Point Easting Northing Height SD Easting SD Northing SD Height 9 Stob Ban summit 214777.2 765443.2 999.727 0.004 0.004 0.017

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 19:28:44 0.004 0.004 -0.042 214777.227 765443.216 999.769 FAUG 25/07/2014 19:28:44 0.003 0.007 0.058 214777.235 765443.209 999.669 INVR 25/07/2014 19:28:44 0.004 0.019 0.008 214777.214 765443.202 999.719 KILN 25/07/2014 19:28:44 0.004 0.017 0.023 214777.213 765443.215 999.703 LCAR 25/07/2014 19:28:44 0.003 0.014 0.019 214777.241 765443.204 999.707 LOCG 25/07/2014 19:28:44 0.003 0.006 -0.033 214777.229 765443.218 999.759 OBAN 25/07/2014 19:28:44 0.006 0.045 -0.099 214777.251 765443.252 999.826

# Point Easting Northing Height SD Easting SD Northing SD Height 10 Stob Ban col 215670.6 765382.6 762.583 0.004 0.003 0.016

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 20:05:44 0.007 0.010 -0.041 215670.625 765382.600 762.624 FAUG 25/07/2014 20:05:44 0.006 0.008 0.063 215670.637 765382.603 762.520 INVR 25/07/2014 20:05:44 0.008 0.016 0.007 215670.615 765382.607 762.576 KILN 25/07/2014 20:05:44 0.007 0.016 0.015 215670.616 765382.613 762.568 LCAR 25/07/2014 20:05:44 0.006 0.011 0.022 215670.639 765382.602 762.561 LOCG 25/07/2014 20:05:44 0.006 0.007 -0.025 215670.629 765382.615 762.607 OBAN 25/07/2014 20:05:44 0.007 0.024 -0.061 215670.648 765382.626 762.644

# Point Easting Northing Height SD Easting SD Northing SD Height 11 Sgurr an Iubhair col 216366.3 765642.9 922.969 0.002 0.006 0.015

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 20:43:44 0.005 0.007 -0.025 216366.349 765642.974 922.994 FAUG 25/07/2014 20:43:44 0.063 0.073 0.099 216366.405 765643.030 922.870 KILN 25/07/2014 20:43:44 0.007 0.004 0.035 216366.353 765642.983 922.934 LCAR 25/07/2014 20:43:44 0.013 0.046 0.037 216366.362 765643.024 922.932 LOCG 25/07/2014 20:43:44 0.061 0.076 -0.069 216366.428 765642.973 923.038

# Point Easting Northing Height SD Easting SD Northing SD Height 12 Sgurr an Iubhair alt summit 216522.2 765513.6 999.716 0.003 0.003 0.012

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 21:02:14 0.003 0.007 -0.016 216522.293 765513.677 999.732 INVR 25/07/2014 21:02:14 0.009 0.075 0.133 216522.304 765513.756 999.583 KILN 25/07/2014 21:02:14 0.007 0.011 0.032 216522.287 765513.688 999.684 LCAR 25/07/2014 21:02:14 0.003 0.006 0.023 216522.302 765513.686 999.693 OBAN 25/07/2014 21:02:14 0.007 0.013 -0.028 216522.308 765513.690 999.744

# Point Easting Northing Height SD Easting SD Northing SD Height 13 Sgurr an Iubhair summit 216521.5 765512.3 999.732 0.002 0.003 0.013

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 21:23:14 0.003 0.008 -0.048 216521.519 765512.358 999.780 FAUG 25/07/2014 21:23:14 0.002 0.008 0.036 216521.528 765512.368 999.697 INVR 25/07/2014 21:23:14 0.004 0.013 0.013 216521.516 765512.368 999.719 KILN 25/07/2014 21:23:14 0.041 0.004 0.013 216521.527 765512.364 999.719 LCAR 25/07/2014 21:23:14 0.002 0.010 0.000 216521.532 765512.352 999.732 LOCG 25/07/2014 21:23:14 0.022 0.039 -0.070 216521.548 765512.328 999.802 OBAN 25/07/2014 21:23:14 0.035 0.010 -0.053 216521.532 765512.369 999.785

# Point Easting Northing Height SD Easting SD Northing SD Height 14 Am Bodach summit 217637.3 765097.7 1031.820 0.002 0.003 0.018

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 22:14:14 0.003 0.003 -0.063 217637.346 765097.700 1031.883 FAUG 25/07/2014 22:14:14 0.003 0.011 0.055 217637.355 765097.711 1031.765 INVR 25/07/2014 22:14:14 0.005 0.005 0.053 217637.347 765097.708 1031.767 KILN 25/07/2014 22:14:14 0.004 0.014 0.021 217637.333 765097.706 1031.798 LCAR 25/07/2014 22:14:14 0.003 0.012 0.004 217637.347 765097.691 1031.816 LOCG 25/07/2014 22:14:14 0.003 0.006 -0.023 217637.345 765097.709 1031.842 OBAN 25/07/2014 22:14:14 0.005 0.013 -0.058 217637.344 765097.716 1031.878

# Point Easting Northing Height SD Easting SD Northing SD Height 15 Am Bodach col 216907.4 765220.6 879.067 0.003 0.003 0.015

Station Date/Time 3D CQ Pos diff Height diff Easting Northing Height ARIS 25/07/2014 22:50:44 0.005 0.007 -0.057 216907.428 765220.637 879.125 FAUG 25/07/2014 22:50:44 0.005 0.004 0.053 216907.429 765220.646 879.015

12 INVR 25/07/2014 22:50:44 0.005 0.014 0.013 216907.413 765220.639 879.055 KILN 25/07/2014 22:50:44 0.008 0.012 -0.006 216907.416 765220.638 879.073 LCAR 25/07/2014 22:50:44 0.004 0.012 0.030 216907.436 765220.636 879.037 LOCG 25/07/2014 22:50:44 0.005 0.011 -0.029 216907.428 765220.654 879.096 OBAN 25/07/2014 22:50:44 0.008 0.020 -0.035 216907.428 765220.663 879.103

Co-ordinate recovery analysis Co-ordinate recovery is a process recommended by Ordnance Survey to validate the accuracy of results from GNSS surveys. The nearest OS Net base station to the survey points on the Mamores was OBAN, just over 40km away. Data from a single survey point was reprocessed using only the OBAN base station as a reference, then that survey point was used as a reference for processing against all seven OS Net base stations within 100km of the western Mamores. This produces position and height figures for each base station that can be compared with the highly accurate OS values for position and height. It is therefore a method of checking the accuracy of GNSS survey results. In order for a result to be accepted as sufficiently accurate for their purposes, Ordnance Survey require results for at least five base stations to be within 0.1m of the OS value. When this method was applied to data from the summit of Mullach nan Coirean East Top, the results were as shown below:

OS Net station km e n u d_ij OBAN 40.6 0.0095 0.0127 0.0208 0.0262 ARIS 52.3 0.0029 -0.0047 0.0274 0.0280 FAUG 48.7 -0.0130 0.0148 -0.0794 0.0818 INVR 96.6 -0.0102 -0.0126 0.0239 0.0289 KILN 55.1 -0.0205 -0.0085 -0.0228 0.0318 LCAR 79.3 0.0106 0.0004 -0.0239 0.0261 LOCG 85.0 -0.0042 0.0135 0.0301 0.0332 where e = easting, n = northing and u = height. The coordinate recovery processing shows that the surveyed height of Mullach nan Coirean East Top is accurate to within 0.03m when measured against six OS Net base stations, with FAUG the only outlier, though that is also within the 0.1m limit specified by Ordnance Survey. When the same method was applied to data from Sgurr an Iubhair summit, the results were as shown below:

OS Net station km e n u d_ij OBAN 42.4 0.0064 0.0090 0.0521 0.0533 ARIS 54.9 -0.0071 -0.0033 0.0480 0.0486 FAUG 47.5 0.0107 -0.0040 -0.1399 0.1404 INVR 95.2 0.0251 0.0205 -0.0446 0.0552 KILN 52.8 -0.0923 -0.0416 -0.0884 0.1345 LCAR 80.3 0.0054 -0.0086 -0.0015 0.0103 LOCG 85.9 0.0247 -0.0305 0.0730 0.0829 These figures are less well clustered, with the FAUG base station generating a figure higher than the required 0.1m. This lower standard of accuracy was to be expected, as satellite data was collected for only 20 minutes on top of Sgurr an Iubhair. Nevertheless, six of the seven base stations generated a height figure within 0.1m of the OS value, and therefore sufficiently accurate to be accepted as valid according to OS stipulations. However, the data collection duration was too short in this case for OS acceptance under OS policy.