Horizon & Obstacle Survey

New obstacle point

Aim the phone's rear camera along the laser's line of sight. Tap Sight to freeze the angles, shoot the laser, then type the reading. How you measured it Level range to base, then tilt to top (best for trees) Slant range straight to the top Level range to base, tilt to top and to base (sloping ground) Type distance and height directly Reads the laser display straight into the field — no soft keyboard fighting you in bright sun. last reuses the previous distance, which is what you want when you're sweeping a tree line at one range. Note

Camera sight

Needs an https address. If you opened this file straight off the phone, the camera stays dark — the angles still work.

Compass check

Phone compasses drift. Stand a pole in the sun, aim the phone straight down its shadow, and tap the button — the true sun bearing is known, so the app can work out the correction.

Working order

1. Stand at the mast. Every distance is measured from there, not from wherever you happen to be.
2. Aim, tap Sight to hold the angles, shoot the laser, key the number in.
3. For anything wide, mark both edges before saving.
4. Work round the compass in order so you can see the gaps closing on the mask.

Trees are the awkward case: the beam scatters off foliage and won't return a clean top. Range the trunk at eye level instead, then tilt to the crown — the default method does exactly that.

Horizon mask

Centre is straight up. The outer ring is the horizon. Shaded area is blocked sky.

Profile

Grey band is where the sun actually goes at this latitude over the year. Anywhere the mask rises into it, you lose sun.

Numbers

Sky view factor is 1 − mean of sin²(horizon elevation) over 360 one-degree sectors, the standard isotropic form. Sun geometry is NOAA's algorithm without refraction, so treat the last two rows as ±0.2°.

Siting class

ISO 19289:2014, published by WMO as No. 8 Annex 1.B. Each variable gets its own class; a site has no single number. Class 1 is a reference site, class 5 is one where measurement meant to represent a wide area should be avoided.

What tripped it

Obstacles ranked by distance-to-height ratio

d/H is ground-referenced, which is how the wind criteria are written. The elevation column is measured from the sensor element you selected on the Site tab.

Station

Leave declination at 0 if your phone already reports true north — most fused Android compasses do. The shadow check on the Measure tab will tell you either way.

Instrument heights

An all-in-one head like a WS90 puts every sensor at one height. Annex 1.B calls that out as a real weakness: mount it at 2 m and the wind is dominated by the surface below it, mount it at 10 m and nothing else complies.

Ground around the station

Slope ° Vegetation height, routinely maintained (cm) Roughness, Davenport class 1 — open sea, fetch ≥ 5 km (z₀ 0.0002) 2 — mud flats, snow, no obstacles (z₀ 0.005) 3 — open flat terrain, grass, few isolated obstacles (z₀ 0.03) 4 — low crops, occasional large obstacles (z₀ 0.10) 5 — high crops, scattered obstacles (z₀ 0.25) 6 — parkland, bushes, numerous obstacles (z₀ 0.5) 7 — suburb or forest (z₀ 1.0) 8 — city centre (z₀ ≥ 2)

Artificial surfaces and water, as a share of ground area

Annex 1.B tests concentric zones around the screen. Pace them out or use imagery.

Points

Take it with you

The survey is kept in this browser between visits where that's allowed. Export before you clear browser data — that's the copy that survives.