Official USCRN Precipitation Algorithm

Each Geonor sensor records three precipitation values and three gauge depths every 5 minutes. It also records, for each wire, the maximum, minimum, and average wire frequences for the hour. This algorithm describes how to derive from these values a single precipitation value for a specific 5 minute period.

For the 5 minute period in question, let P1, P2, P3 be the three precipitation values, in mm, and d1, d2, and d3 the three gauge depths, in mm. Let the maximum, minimum, and average wire frequences for the hour be denoted by F1min, F2min, F3min, F1max, F2max, F3max, F1avg, F2avg, and F3avg. Also let d1prev, d2prev, and d3prev be the gauge depths from the previous 5 minute period.

Each of the Pi's is either zero, some postive number, or is missing. (A missing value can be the result of a temporary equipment malfunction, or an error in data transmission; missing values are indicated by a value of 6999 or -6999.) We say that a Pi is present if it is not zero and is not missing --- i.e. it is some non-zero value other than 6999 or -6999.

We will also need the pairwise differences of each pair of precipitation values (omit any of these involving precipitation values that are not present):

D12 = | P1 - P2 |
D23 = | P2 - P3 |
D31 = | P3 - P1 |
For each of the three differences Dij, we say that Dij is "within tolerance" if Dij ≤ 0.3.

In some situations we use the following terminology: we say that a Pi (i=1,2,3) is valid if |di - diprev| ≥ 0.3 and Fimax - Fimin > 2.

With the above terminology we can now state the algorithm for the official USCRN precipitation value as follows:

• If any of P1, P2, P3 is greater than 25, then the official precipitation is specified as "missing"
• If all three of P1, P2, P3 are present, and they are all less than or equal to 25, and
• if all three of the Dij are within tolerance, then the official USCRN precipitation value is the median of P1,P2,P3.
• if exactly two of the Dij are within tolerance, then the official USCRN precipitation value is the median of P1,P2,P3.
• if exactly one of the Dij is within tolerance, then the official USCRN precipitation value is the average of the two precipitation values whose difference is within tolerance.
• if none of the Dij are within tolerance, then the official USCRN precipitation value is specified as "missing"
• If exactly two of P1, P2, P3 are present, and they are both less than or equal to 25, and
• If both of the present Pi values are ≤ 0.3 and
• if both of these Pi values are valid, then the official USCRN precipitation value is the average of these two values
• if exactly one of these Pi values is valid, then the official USCRN precipitation value is this one valid value
• if neither of these Pi values is valid, then the official USCRN precipitation is specified as "missing"
• If at least one of the present Pi values is > 0.3 and
• if the difference between the two present Pi values is within tolerence, then the official USCRN precipitation value is the average of these two values
• if the difference between the two present Pi values is > 0.3, then the official USCRN precipitation is specified as "missing"
• If exactly one of P1, P2, P3 are present, and it is less than 25, and
• if this one present value is valid, the official USCRN precipitation value is this one valid value
• if this one present value is not valid, then the official USCRN precipitation is specified as "missing"
• If none of P1, P2, P3 are present, then the official USCRN precipitation is specified as "missing"