| Description: | During numerous periods within the days listed above, individual soil
moisture probes indicate small positive or else negative values when
soil moisture is high (greater than 35%). This situation has occured
since the present EBBR unit was installed on 17 July 1996. The cause
of the problem is inadequate range in the calibration curve equation.
Cement soil is somewhat unique amongst the EBBR sites, as the soil is
very sandy and porous; it can hold a larger amount of water per volume
than the other soils. This high a soil moisture cannot be obtained with
the calibration soil used by REBS. Therefore, the soil moisture equations
need to be manipulated to allow larger soil moistures to be calculated.
Much of the data from January 1998 is corrupted by this problem,
making changes in the equations prudent.
The soil moisture data must be inspected by the data user to see when
soil moisture values for one or more probes is inconsistent with the
others.
Recalculation of ave_shf, e, and h must be made using only the soil
moisture sets with correct soil moisture values.
Affected data values are (# for probe number):
15 minute: rr_sm#
30 minute: sm#, c_shf#, cs#, ces#, g#, ave_shf, e, h
Sensible, latent, and soil heat fluxes can be recalculated using the soil
probe sets that provide correct data. For example, if soil moisture 2 is
incorrect,
ave_shf = (g1 + g3 + g4 + g5)/4
e = -(q + ave_shf)/(1 +bowen)
h = -(e + ave_shf +q),
If soil moisture 2 and 4 are incorrect,
ave_shf = (g1 + g3 + g5)/3
e = -(q + ave_shf)/(1 +bowen)
h = -(e + ave_shf +q),
If soil moisture 2, 4, and 5 are incorrect,
ave_shf = (g1 + g3)/2
e = -(q + ave_shf)/(1 +bowen)
h = -(e + ave_shf +q),
etc.
On 5 May 1998 at 1815 GMT a calibration coefficient was changed in the CR10
program as a result of a BCR by the mentor. This coefficient has helped
reduce the least severe problems but has not eliminated problems from
large negative soil moistures measured even once during the integration
period. However, now the incorrect average soil heat flow, latent heat
flux, and sensible heat flux are so large, negative or positive, that they
cannot be mistaken as being correct.
The EBBR unit was replaced with a recalibrated system on 1 April 1999.
The previous unit experienced soil moisture problems the entire time
(almost 3 years) that the system was installed because of the inadequacy
of the soil moisture sensor calibrations. |