LDS01 / WH54 Water/Snow Measurement

[PaulMy]

After a month of using the Laser Distance Meter along with the GW2000, my initial observations:

During typical snowing the LDS seems quite accurate to +/- 0.1 cm accumulation on live snowfall and on snow depth. This compares well to my manual daily snow readings.

Periods of no new snow can see a decrease in depth but usually no more than 0.1 cm in a 5-minute interval, but there are occasional -0.2 cm, and that would be compaction or melt in warmer or sunny weather. Again similar to the manual reading

Now in periods of warmer weather and rain it becomes less reliable.
I measure my manual snowfall and snowpack on a wooden deck, and make observation and good judgement if that is reasonably valid for the open 5-acre filed behind. This morning there was still about 7 cm on part of the deck and in the field. The LDS01 is mounted above the wooden deck and underneath the laser it was bare - deck was about 50/50 snowpack/bare. The LDS01 had been measuring the distance at 894 mm with no snowpack (clear from laser to deck). Then with some light rain and likely droplets bouncing from the deck and I've had snowfall recorded and in a period of 45 minutes from 0.1 to 0.8 mm and then back to 0.0. CMX recorded the same 8 mm high laser depth but only 0.5 mm Snow24h.

Not ready yet to publish on my winter summary!

Enjoy,
Paul

[sutne]

Paul,
I wonder how you manually measure snowdepth with 1mm precision?
The snow surface is very uneven. When using a ruler I can have problems to decide which cm to use.
The only problem I have with the LDS is when it is around 0 C˚, it rains and snows and the snow on top of the LDS melts and forms a hollow where it is measuring.

In the future I will drop the mm and only present snowdepth rounded to cm.

[PaulMy]

@Steinar,

I wonder how you manually measure snowdepth with 1mm precision?
The snow surface is very uneven. When using a ruler I can have problems to decide which cm to use.

I agree, hard to tell especially on fresh snowfall. With the ruler in the snow I place my thumb on the ruler where the snow level is and then pull out the ruler and that gives an easier to read point of reference often to 1/2 mm, and take several measurements, and that gives me an acceptable snow depth, rounding to the nearest whole cm. I generally record in 1 cm increment. An exception is when there is a trace of snow during the day and that may not be visible at the 8:00 am reading and for these that was recorded as 'T' trace for the CoCoRaHS reporting. When CMX changed the diary and that would not permit a 'T' entry but did allow for decimals, I started to use 0.x for trace or less than 1 cm measurements as it counts as a snow day.

The LDS01 has brought in the 0.1 increment, and as keen weather data observers we use it
But even this precise instrument has difficulty with it as it often jumps up and down 0.1 mm or more.

I have the LDS01 settings as Total Height 895 mm. Now that the snow is gone from underneath the laser I regularly see somewhat incorrect measurements - Air as 902 and Depth as 0, Air 893 and Depth 0. I suspect this is part of the Ecowitt's internal methodology to overcome abnormalities. I did not see these larger variances during snowfall.

The only problem I have with the LDS is when it is around 0 C˚, it rains and snows and the snow on top of the LDS melts and forms a hollow where it is measuring.

During periods of no new snow and some melting, I have also seen the hollow below the sensor in about a 5 to 8 cm circle. Coincidence, or affect of laser on the snow?!?

Enjoy,
Paul

[sutne]

Coincidence, or affect of laser on the snow?!?

I think it is created by the rain/melting snow.

[mcrossley]

Drips from the sensor?

[sutne]

Yes, and the plank it is attached to.
I have plans for next season to make a small roof and draining along the plank.

[PaulMy]

I am a little confused on the LDS01 Calibration. When I first got the LDS01 set up it was over an existing snowpack and I set the Total height to what I thought was pretty accurate. The snow 'depth' and 'air' data at the time seemed quite reasonable and stayed that way for the time we had snow and snowpack.

While we don't have any snow now I relocated the sensor to a better location, and I am getting conflicting readings as to depth and air. As best as I can measure from the laser in the device to the floor is 900 mm, I reset the Total Height at 900 and that soon indicated Depth = 10 and Air = 890. I then changed Total Height to 890 and that shows Depth 0 and Air between 893 and 899. Four hours ago I set the Total Height again at 900 and the Depth has fluctuated between 0 and 4, and Air 900 to 896. I understand the measurement to 0.1 of a mm is not practical, but showing snow up to 4 mm when it is 3°C and bright sunshine is not correct.
My calibration settings are:
Offset = 0 mm
Total Height: 900 mm
Data Filter Factor: 0

Any pointers so I can get organized for next snow season?

Enjoy,
Paul

[sutne]

Paul,
I have seen the same with my LDS01, but I have around 60 cm of snow and the snow surface is not quite even.
I round up my readings in my charts to cm.
Then without any visible change in the snow, the readings sometimes flicker between two cm.
I notice the same behaviour for the nearest Official Met Office.

https://rjoand.utnet.no/snowcharts.htm#hourlysnow

[PaulMy]

After a steady period of showing 895 'Air' I have recalibrated to 'Total Height' 895 and that has corrected the snow 'Depth' to 0. There is still some 'Air' fluctuation but the Depth has stayed at 0. This is much better than the up to 12 mm (1.2 cm) fluctuation I had seen.

I think the reason for the fluctuation is the wood base and the laser behavior on such a surface, like discussed here https://www.wxforum.net/index.php?actio ... ts;u=18125.
I made sure the board the LDS01 is installed on is level, but having the LDS01/laser beam that is screwed to the board perfectly level is another matter. And possibly the laser beam onto unpainted wood may react differently compared to other surfaces like snow or painted snowboard.

I would need more uniform readings before I would convert my live CMX to LDS01 snow measuring. Unfortunately our snow is likely over for this season.

Enjoy,
Paul