Mapping Mountains – Trimble Surveys – Elenydd

 

22.10.20  Allt Goch (SN 671 773) 

LIDAR image of Allt Goch (SN 671 773)

This hill was the third of seven that I planned on visiting during the day, and prior to this I had analysed its numerical details via LIDAR.  LIDAR shows the upper part of the hill to consist of a slender mound running in a north to south direction and the bwlch positioned to the east north-east of the summit on or beside the A4120 road. 

A conveniently placed bridleway marches across this hill from north to south and this gave an easy option for the ascent.  I found parking on the grass verge beside the road a few metres west from where the bridleway started. 

The bridleway consists of a track and as I gained height on it the first flashes of morning light highlighted parts of the surrounding land.  Prior to this the skies had been overcast, and although the higher tops to the east were still bathed in clag, I had spotted a number of the hills I planned on visiting later in the day and their summits were all below the cloud base. 

Autumnal light can be wonderful with it highlighting the colourful display on trees, when their golden yellows and rusted reds are mixed along with browns and oranges giving a myriad of colour.  This is only enhanced when grey sky predominates, as this forms an ideal backdrop for autumnal light.  Although the cloud had started to break up and sunlight gave intermittent colour it wasn’t until later in the day that I was treated this magical display of autumnal light. 

The track soon led to a gate and this gave access to the upper field where the summit of the hill is situated.  Once on the high point I assessed the lay of land for Trimble placement, two points vied for the accolade of summit position, each only a couple of metres from the other.  Having chosen what I judged to be the highest I set the Trimble up to gather data. 

Gathering data at the summit of Allt Goch

During data collection I stood away from the equipment and scribbled all necessary detail in my notebook, including the measurement offset, name of hill, point of survey (summit or bwlch), time the equipment was activated to gather data, number of satellites logged on to, estimated margin of positional uncertainty, feature at summit or bwlch, number of points gathered and the time duration of the survey. 

All of the above passes a minute or two and as the normal allotted time for each survey is five minutes, the time spent at the summit soon passes, and today I also kept an eye on four horses, and although they has spotted me they thankfully kept their distance.  Once five minutes of data were gathered and stored I headed back up to the summit and closed the equipment down, took a few photos and packed it away. 

The Trimble set-up position at the summit of Allt Goch

Before leaving the summit I looked out toward my next hill of the day; Penpegws (SN 702 755).  This was to my south-east and whereas the first three hills of the day were accessed from the convenience of the A4120 road, the remaining four hills all had starting points from narrow lanes, and with each positioned close to a lake it was an area that I was looking forward to investigating. 

 

Survey Result: 

 

Allt Goch  

Summit Height:  238.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 67119 77395 (Trimble GeoXH 6000) 

Bwlch Height:  192.1m (LIDAR)

Bwlch Grid Reference:  SN 67881 77648 & SN 67876 77643 (LIDAR)

Drop:  46.7m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  19.56% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet