Ed Andreas and Keran Claffey. have provided 1 hour estimates of TRH and sonic anemometer heights above snow.
The sensor height data values have been added to the 1 hour SHEBA PAM dataset with the following variable names:
| Variable | Description |
|---|---|
| Z.TRH.meas | TRH sensor height above snow, interpolated from direct measurements, meters |
| Z.TRH.snowline | TRH sensor height above snow, interpolated using snow-line data, meters |
| Z.sonic.meas | sonic anemometer height above snow, interpolated from direct measurements, meters |
| Z.sonic.snowline | sonic anemometer height above snow, interpolated using snow-line data, meters |
The following documentation on the sensor height estimates was provided by Keran and Ed.
A Note on Time:
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date/time |
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Year |
Month |
Day |
Hour |
Minutes |
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Calc |
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1997 |
10 |
14 |
0 |
30 |
10/14/1997 0:30 |
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1997 |
10 |
14 |
1 |
30 |
10/14/1997 1:30 |
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1997 |
10 |
14 |
2 |
30 |
10/14/1997 2:30 |
|
1997 |
10 |
14 |
3 |
30 |
10/14/1997 3:30 |
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1997 |
10 |
14 |
4 |
30 |
10/14/1997 4:30 |
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1997 |
10 |
14 |
5 |
30 |
10/14/1997 5:30 |
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1997 |
10 |
14 |
6 |
30 |
10/14/1997 6:30 |
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1997 |
10 |
14 |
7 |
30 |
10/14/1997 7:30 |
|
1997 |
10 |
14 |
8 |
30 |
10/14/1997 8:30 |
The original PAM data files included Year, Month, Day, Hour, minute columns as above. From these columns we made a date/time (Calc) column that reflected these given parameters. This date/time calc column is the only time column that appears in our data file.
According to the PAM project report, hourly averages are centered on the half hour; in other words, hourly averages are centered around the given time. 10/14/1997 2:30 means the averages are from data collected from 1:00 to 2:00 on 10/14/1997.
For all of the concern of exact times above, the times of the PAM instrument height measurements are not given in the PAM project report and the times of the snow line/stake measurements are not readily available. In figuring the interpolations, I used the time of 13:00 for when these measurements were made.
Instrument Heights above Snow
Atlanta:
There are two columns for TRH height and Sonic height. The first column (measured) contains actual measurements of height and the interpolation between these measurements. During periods of placement that only one measurement was made, this measurement was reported throughout the whole period of placement. (i.e., the sonic height was measured during the initial deployment of Atlanta, and not measured again until after an ATI sonic had replaced the Gill sonic. Since the ATI sonic was installed at a different height, no interpolation was attempted while the Gill sonic was in place. The initial measured height was reported in the measured column for the entire period of the Gill sonic placement.)
The PAM log contains Snow Line information from the Atlanta site. In comparing both Baltimore and Atlanta snow line data with the measured TRH/Sonic heights, we found that the TRH/Sonic heights decreased at about ½ of the snow line data depth increase. At Baltimore we found that this 1 to 2 correspondence effect ended after November. However, at Atlanta we found that this effect continued into April. During the melt season, at both Baltimore and Atlanta, there was a close 1 to 1 correspondence between the snow line data and the measured TRH/Sonic height data. We suspect that the initial one (TRH/Sonic) to two (Snow line) is caused because the snow is filling in the valleys (or voids) in the uneven ice surface until the snow surface is level. After the snow surface is leveled, the snow increases and decreases at the same rate on the snow line as under the TRH/Sonic data.
SONIC:
We only have the initial reading for the installation of the Gill Sonic height until this was changed to an ATI Sonic in April. We used the Snow line during this period to determine the changing height. We lined up the Snow/Sonic height at the 4/11/98 reading (when the ATI was installed) and again used the snow line (because of the many more snow readings then measured height readings) to determine changes in Sonic height until 6/22/98. These heights lined up well with the measured Sonic heights. After 6/22/98 the measured Sonic height and height based on the snow line diverged too much to continue using the snow line depths as an indicator to determine Sonic height, so we used the measured Sonic height. This divergence after 6/22/98 is not surprising as the snow line begins to include many melt ponds.
TRH Sensor:
Because of the many more snow line measurements then TRH height measurements, we used the snow line to determine the TRH height. These heights compared well until 6/22/98, the beginning of the melt season. After 6/22/98 there were no measurements of TRH height made until 8/29/98. The difference between the change in height of the TRH and the Sonic differ substantially between 6/22/98 and 8/28/98. It was felt that the TRH might have been measured above a surface modified by the effects of the placing ablation shielding under the Atlanta Tripod. Because of this, we based the TRH heights made after 6/22/98 on the measured Sonic heights.
Cleveland:
The Cleveland snow line showed a steady snow depth (less then a 4.4 cm change) while the PAM station was deployed. Therefore we used the initial measurements of instrument height for the whole period that Cleveland was deployed.
Seattle:
We are using the Sonic/TRH height measurements made at the site. There was only one measurement made for TRH height during this period. When first installed, on 4/16/98, a Gill Sonic was used and was measured as being 3.45m above the snow surface. On 4/22/98 an ATI Sonic was installed at 2.90m above the snow surface. The second measurement made on 5/16 was 2.87m, a change of only 0.03. These measurements were used in determining the height of the Sonic above the snow surface for the duration of Seattle.
The mainline snow line did run near Seattle; however, the main line was 300 m long, meaning that most of the line was far away from Seattle. If better 'instrument above snow' measurements are needed, it would be possible to take the section of the main line closest to Seattle and use these snow measurements to better estimate the instrument heights.
Maui:
There are no snow measurements other then the instrument height measurements taken near Maui, therefore we can only use interpolation between the actual height measurements.
Baltimore:
There are two columns for TRH height and Sonic height. The first column (measured) contains actual measurements of height and the interpolation between these measurements. During periods of placement that only one measurement was made, this measurement was reported throughout the whole period of placement. (i.e., the sonic height was measured during the initial deployment of Baltimore, and not measured again until after an ATI sonic had replaced the Gill sonic. Since the ATI sonic was installed at a different height, no interpolation was attempted while the Gill sonic was in place. The initial measured height was reported in the measured column for the entire period of the Gill sonic placement.)
The second column is modification of the heights measurements based on nearby snow depth measurements made on the Baltimore Snow Line.
The PAM log contains Snow Line information from the Baltimore site. In comparing both Baltimore and Atlanta snow line data with the measured TRH/Sonic heights, we found that the TRH/Sonic heights decreased at about ½ of the snow line data depth increase. At Baltimore we found that this 1 to 2 correspondence (during increasing snow depth) ended after November. During the melt season, at both Baltimore and Atlanta, there was a close 1 to 1 correspondence between the snow line data and the measured TRH/Sonic height data. We suspect that the initial one (TRH/Sonic) to two (Snow line) is caused because the snow is filling in the valleys (or voids) in the uneven ice surface until the snow surface appears flat. After the snow surface flattens out, the snow increases and decreases at the same rate on the snow line as under the TRH/Sonic data.
SONIC:
We only have the initial reading for the installation of the Gill Sonic height until this was changed to an ATI Sonic in April. We used the Snow line during this period to determine the changing height. We lined up the Snow/Sonic height at the 5/15/98 reading and again used the snow line (because of the many more snow readings then measured height readings) to determine changes in Sonic height. These heights lined up well with the measured Sonic heights. The last snow depth was measured on 7/9/98. After this date we used the measured sonic heights.
TRH Sensor:
Because of the many more snow line measurements then TRH height measurements, we used the snow line to determine the TRH height. There was only one place where the snow measurements did not line up well with the measured TRH height. The 5/15/98 measured TRH height was significantly below the snow line height. Because of this, we chose to use the measured TRH height on 5/15/98 then continued to use the Snow line based height after this date. The last snow depth was measured on 7/9/98. After this date we used the measured TRH heights.
Florida:
There are two columns for TRH height and Sonic height. The first column (measured) contains actual measurements of height and the interpolation between these measurements. During periods of placement that only one measurement was made, this measurement was reported throughout the whole period of placement. (i.e., during the period of placement of Florida at the original site, from 10/22/1997 to 04/01/1998, the instrument heights were measured only once, on 10/25/1997. This height was then reported in the measured column for the entire period of this placement.)
The second column is modification of the heights measurements based on nearby snow depth measurements. The closest measured snow to Florida is the Pittsburgh mass balance stakes.
We used the increase/decrease in average snow depth at Pittsburgh to determine the change in height through April 1st, when Florida was moved. Between April 1st and April 20th (Florida was moved to its summer location on April 20th) there were no measurements taken of the TRH height, therefore we have cannot determine the height the TRH sensor was between these two moves. There was one measurement made of Sonic height during this time period. We used this measurement along with the changing snow depth at Pittsburgh to estimate the height of the Sonic during this period.
After being moved to its summer home on April 20th, the measured heights of both the TRH sensor and the Sonic sensor do not change at the same rates as the snow depth at Pittsburgh. We suspect that this is because Florida was placed near (on) a ridge (high point) with only a small amount of snow underneath it. Therefore, from April 20th on, we depend solely upon the interpolation between the measured heights of these instruments. (It is worth noting that there were many more measurements of instrument height made after April 20th then before.)