Metadata for Ameriflux intercomparison files
missing data is -999 for all files.
All files use a comma as delimiter between columns
Local time is Central Standard Time, -6 UTC, all times are reported in UTC here
afiles – 10Hz data, half-hourly files
Top of tower, high frequency data
File name: /afiles/03ddd/hl03ddd.hhmm.csv
Files are gzipped to save disk space /afiles/03ddd/hl03ddd.hhmm.csv.gz
Year - 2003
DOY - Day of Year (236-248)
hhmm – time in format hhmm, UTC
Sec – Second x.x
Ux – into sonic wind speed, m/s (positive is toward transducer)
Uy – across sonic wind speed, m/s (positive is from right to left)
Uz – vertical wind speed, m/s (positive is upwards)
Ts – sonic virtual temp, degrees C
Csat_diag – CSAT-3 diagnostic code (<63 is good)
CO2 – LI-6262 analog out, mv
H2O – LI-6262 analog out, mv
LI_P – Licor pressure, kPA
LI_T – Licor temperature, degrees C
Wspd – computed horizontal wind speed, m/s
WDir – computed horizontal wind direction, degrees from true north
cal – daily computed data, one file
Slope and intercept to convert LI-6262 H2O and CO2 mv to mixing ratios (equations are below). The slope and
intercept for each day is computed by computing a regression of 3-day (centered on the day of interest)
calibrated 3 minute interpolated CO2 mixing ratio at 36 m from the high precision CO2 profiler to 3 minute
averaged temperature, pressure and water vapor -corrected 3-minute averaged flux licor output.
File name: /cal/hl03.cal.csv
Year - 2003
DOY - Day of Year (236-248)
Mq_h2o – slope of water vapor fit
Bq_h2o – intercept of water vapor fit
Mc_co2 – slope of CO2 fit
Bc_co2 – intercept of CO2 fit
To calculate high frequency water vapor mixing ratio:
FUNCTION calc_h2o,qv,tl,pl,mq,bq
;qv = h2o voltage
;tl = licor temp in degrees K (note units!)
;pl = licor pressure in mb (note units!)
;mq = m slope from calibration
;bq = b intercept from calibration
;output = water vapor mixing ratio in g/kg
tref = 273.15
pref = 1013.0
qref = 0.0
eps = 18.016/28.97
bigpiece = (mq*qv*pref/pl+bq)*(tl/tref) + qref
q = bigpiece/(1.0-bigpiece*(1.0/(1000.0*eps)))
return,q
END
Once you compute water vapor mixing ratio, you can compute CO2 mixing ratio
FUNCTION calc_co2,cv,tl,pl,mc,bc,q
;qv = co2 voltage
;tl = licor temp in K (note units!)
;pl = licor pressure in mb (note units!)
;mc = m slope from calibration
;bc = b intercept from calibration
;q = dry air mixing ratio (g/kg)
;output = CO2 mixing ratio in ppm (umol/mol)
tref = 273.15
pref = 1013.0
k = -0.1
cref = 0.0
rinit = q/1000.0*28.97/18.016
c = ((mc*(cv*pref/pl)+bc)*(tl/tref)+cref)*(1+rinit)+k*(tl-tref)
return,c
END
bfiles – 1 minute data (1 second collection, 1 minute avg), daily files
Top of tower non-flux sensors
File name: /bfiles/hl03ddd.b.csv
Year - 2003
DOY – Day of Year (236-248)
hhmm – time, UTC
t – Air temperature (36 m), degrees C
atm_p – atmospheric pressure (36 m), mb
rh – relative humidity (36 m), %
dew_pt – Dew Point (36 m), degrees C
net rad – Net Radiation (36 m), W/m2
Par – direct PAR (36 m), old K&Z sensor – reads high I think, umol/m2/s
Leaf wetness – leaf wetness, KOhms
bvolt – Tower voltage, V
h2o – H2O mixing ratio (36 m), g/kg
Total PAR – total PAR (36 m), delta T sensor, umol/m2/s (use this PAR)
Dif PAR – diffuse PAR (36 m), delta T sensor, umol/m2/s
cfiles – 3 minute data (1 second collection, avg of last 1 minute), daily files
This is raw data from the high precision profiler (average of CO2 voltage, temp and pressure for last minute of
three minute sample). High precision CO2 in computed by creating a second order polynomial with each set of
cal gasses (ID 8,9,10) run every two hours and interpolating the transfer function with time (system is zeroed
out with ID 8 gas every 42 minutes). The LI-6252 profiler is run in differential mode against a reference CO2
(same gas as used in ID 8). Sample air is drawn by 6 L/min pump through 40-70 m of Synflex tubing and sent
to profiler at 100 ml/min. Sample is dried with Nafion tube dryer run with countercurrent of drierite-dried N2
and used dry sample air. Mixing ratios of gasses for the time period of interest were: 8 (and ref gas): 392.67, 9:
336.51 10: 428.18 ppm. Pressure and temperature corrections are as follows from the Licor 6252 manual, with
reference P set to 101.3 kPa and reference T set to 273.15 K. See micromet file for heights of levels 1-7.
File name: /cfiles/hl03ddd.c.csv
Year - 2003
DOY – Day of Year (236-248)
hhmm – time, UTC
ID – Level (levels 1-7, 8 is reference CO2, 9 is low standard, 10 is high standard)
li_t (Licor Temp)
li_p (Licor Press)
co2 (CO2 Voltage)
micromet – half hourly data, one file
Processed, half-hourly average non-flux data (including precip)
File name: /met/hl03.met.csv
Column
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Name
Year
Month
DOM
UTC
DOY
F_day
CO2_36m
CO2_21m
CO2_14m
CO2_7.6m
CO2_3m
CO2_1.8m
CO2_0.6m
Atm_P_36m
Wind_Spd_36m
Wind_Spd_20m
Wind_Deg_36m
Wind_Deg_20m
Q_36m
Q_20m
Q_10m
Q_2m
RH_36m
RH_20m
RH_10m
RH_2m
Dew_Pt_36m
Dew_Pt_20m
Description
Year
Month
Day of Month
Universal Time (Z)
Day of Year
Fraction of Day
CO2 concentration at 36m/118ft
CO2 concentration at 21m/70ft
CO2 concentration at 14m/45ft
CO2 concentration at 7.6m/25ft
CO2 concentration at 3m/10ft
CO2 concentration at 1.8m/6ft
CO2 concentration at 0.6m/2ft
Air pressure at 36m/118ft
Wind speed at 36m/118ft
Wind speed at 20m/65ft
Wind direction at 36m/115ft
Wind direction at 20m/65ft
H2O mixing ratio at 36m/118ft
H2O mixing ratio at 20m/65ft
H2O mixing ratio at 10m/32ft
H2O mixing ratio at 2m/6ft
Relative humidity at 36m/118ft
Relative humidity at 20m/65ft
Relative humidity at 10m/32ft
Relative humidity at 2m/6ft
Dew point at 36m/118ft
Dew point at 20m/65ft
Unit
Year
Month
Day
Hour
Day
ppm
ppm
ppm
ppm
ppm
ppm
ppm
mb
m/s
m/s
deg
deg
g/kg
g/kg
g/kg
g/kg
percent
percent
percent
percent
degrees C
degrees C
Range/Notes
2000-3000
8-9
24-31/1-5
0.0-23.5
236-248
0-1
0-360
0-360
0-100
0-100
0-100
0-100
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
Dew_Pt_10m
Dew_Pt_2m
Precip
Throughfall
Leaf wetness
T_36m
T_30m
T_23m
T_20m
T_15m
T_10m
T_7.6m
T_1.8m
T_0.6m
T_shed
Ta_100cm
Ta_50cm
Ta_25cm
Ta_5cm
SoilT_0cm
SoilT_5cm
SoilT_10cm
SoilT_25cm
SoilT_50cm
SoilT_100cm
SoilLWC_5cm
SoilLWC_10cm
SoilLWC_20cm
SoilLWC_50cm
SoilLWC_100cm
PAR_20m
PAR_40m
VPD_36m
VPD_20m
VPD_10m
VPD_2m
W_36m
PAR_36m_2
PAR_36m_Diff
Storage
69
70
NetRad
G
Dew point at 10m/32ft
Dew point at 2m/6ft
Total precipitation
Precip at bottom of tower
Leaf wetness at 36m/118ft
Air temperature – 36m/118ft
Air temperature – 30m/100ft
Air temperature – 23m/75ft
Air temperature – 20m/65ft
Air temperature – 15m/50ft
Air temperature – 10m/32ft
Air temperature – 7.6m/25ft
Air temperature – 1.8m/6ft
Air temperature – 0.6m/2ft
Temperature in control shed
Air temperature – 100cm/40in
Air temperature – 50cm/20in
Air temperature – 25cm/10in
Air temperature – 5cm/2in
Soil temperature – 0cm/0in
Soil temperature – 5cm/2in
Soil temperature – 10cm/4in
Soil temperature – 25cm/10in
Soil temperature – 50cm/20in
Soil temperature – 100cm/40in
Soil moisture content – 5cm
Soil moisture content – 10cm
Soil moisture content – 20cm
Soil moisture content – 50cm
Soil moisture content – 100cm
Below canopy PAR (6m/20ft)
Below canopy PAR (12m/40ft)
Vapor Pressure Deficit - 36m
Vapor Pressure Deficit - 20m
Vapor Pressure Deficit - 10m
Vapor Pressure Deficit - 2m
Mean vertical velocity
Delta_T total PAR
Delta_T diffuse PAR
Rate of change CO2 storage
36 m
Net radiation (NR-LITE) 36 m
Soil heat flux – 75 mm
degrees C
degrees C
cm
cm
No snow adapter
KOhms
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
Disconnected in Jan
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
degrees C
vol fraction 0-1
vol fraction 0-1
vol fraction 0-1
vol fraction 0-1
vol fraction 0-1
umol/m2s
umol/m2s
kPa
kPa
kPa
kPa
m/s
umol/m2s
installed 6/27/2003
umol/m2s
installed 6/27/2003
umol/m2s
W/m2
W/m2
storage corrected
flux – new file, half hourly data, one file
Computed 30 minute fluxes, in both kinematic and standard units. Flux values for both local rotation (mean W
= 0) and long-term rotation (fit of theta to phi) are given.
The long term rotation fit for 2003 to date is: theta = (-0.06898 * sin (phi + 1.43082)) - (0.00135 * phi^3) +
(0.00209 * phi^2) + (0.00924 * phi) + 0.01608
High frequency correction factors are given but not applied. Simply multiply CO2 fluxes by C_cfactor and
H2O fluxes by Q_cfactor to find frequency loss corrected fluxes.
Filename: /flux/hl03.flx.csv
Year - 2003
DOY – Day of Year (236-248)
hhmm – time, UTC
CO2 Flux, local rotation, ppm m/s
CO2 Flux, final rotation, ppm m/s
CO2 Flux, local rotation, umol/m2/s
CO2 Flux, final rotation, umol/m2/s
H2O Flux, local rotation, g/kg m/s
H2O Flux, final rotation, g/kg m/s
H2O Flux, local rotation, W/m2
H2O Flux, final rotation, W/m2
T Flux, local rotation, K m/s
T Flux, final rotation, K m/s
T Flux, local rotation, W/m2
T Flux, final rotation, W/m2
Momentum flux, u*^2, local rotation, m2/s2
Momentum flux, u*^2, final rotation, m2/s2
Momentum Flux, local rotation, Pa
Momentum Flux, final rotation, Pa
Phi, horizontal rotation angle, radians
Theta, local vertical rotation angle to make mean W = 0
Theta_model, based on long-term fit of phi to theta
Lag_c, Lagged covariance between CO2 and W, s
Lag_q, lagged covariance between H2O and W, s
C_Cfactor, spectral correction factor for CO2 flux (multiply C flux by it)
Cflag, spectral correction factor flag, 0 = good, -70 = filled
Q_cfactor, spectral correction factor for H2O flux (multiply Q flux by it)
Qflag, spectral correction factor flag, 0 = good, -70 = filled
gold – fluxes computed from gold file, half hourly data, one file
/gold/goldflux.csv
Computed 30 minute fluxes from gold file raw data, first cut, no screening. Only local rotation (mean W = 0) is
applied. High frequency correction factors are given and applied. Simply divide CO2 fluxes by C_cfactor and
H2O fluxes by Q_cfactor to find uncorrected fluxes. This is preliminary, since I am not sure if retooling my
code to accept Gold files introduced any bugs or constants I didn’t change.
hhmm – Time, unknown timezone, 12:00-21:00
CO2 flux, umol/mol * m/s
H2O flux, mmol/mol * m/s
T flux, K * m/s
Momentum flux, m2/s2
Phi, horizontal rotation angle, radians
Theta, local vertical rotation angle to make mean W = 0
Lag_c, Lagged covariance between CO2 and W, s
Lag_q, lagged covariance between H2O and W, s
C_Cfactor, spectral correction factor for CO2 flux (multiply C flux by it)
Cflag, spectral correction factor flag, 0 = good, another number = what spectral correction was, but not used
because less than 1 or greater than threshold (1 is used instead)
Q_cfactor, spectral correction factor for H2O flux (multiply Q flux by it)
Qflag, spectral correction factor flag, 0 = good, another number = what spectral correction was, but not used
because less than 1 or greater than threshold (1 is used instead)
Ancillary information
> > 1.
Are your 30-min averages written at the beginning or the end of the
> > designated time stamp?,
Beginning of time stamp
> > 2.
Please describe your flux processing program, i.e., how your
> > coordinate rotation is calculated, any filtering of data (variance filters,
> > u* filters, etc.), averaging operator (block-averaging, linear detrend,
> > recursive filter, etc..), what type of high frequency corrections were
> > made, estimates of zero plane displacement, roughness length,
The flux processing is similar for WLEF, Willow Creek, Lost Creek, and Sylvania. It is based on the methods
described in: Berger, B.W., Davis, K.J., Yi, C., 2001. Long-term carbon dioxide fluxes from a very tall tower
in a northern forest: Flux measurement methodology. J. Atmos. Ocean. Tech. 18, 529-542. That paper is also in
this directory.
Step 1. Multiply CO2 and H2O analog mv data by the calibration slope and intercept computed with the CO2
profiler as described above (in the cal section).
Step 2. Rotate wind data. For “local” rotation (first run), the data is oriented into the mean horizontal wind (so
that mean V = 0), producing a phi, and aligned so that mean W = 0, producing a theta. At the end of each year
(or life of instrument), we fit phi and theta (planar fit) with a combination sine and cubic fit (see the equation in
the flux section above), so as to model theta as a function of phi. For “final” rotation runs, the data is oriented
into the mean wind and then vertically oriented using the modeled theta.
Step 3. Wind and scalar data are linearly detrended.
Step 4. Lagged covariances between W and T,C,Q are computed. The peak covariance within an acceptable
tolerance window ( +/- 10 seconds for T, 20 seconds for C and Q) for each scalar is used to compute flux.
Missing lag data is filled with 20 day diurnal median.
Step 5. Variance filters are applied. Fluxes and frequency corrections are not computed if the variance in
temperature is > 2.5 degrees, or the variance in W is > 3.0 m/s. Also fluxes are not computed when the mean
licor pressure is greater than 100.0 kPa (i.e. bad pump)
Step 6. Frequency corrections are applied. We only apply high frequency corrections. For water vapor flux, we
degrade (as described in Berger et al 2001) the temperature turbulent power spectrum to match that of water
vapor (using a square wavelet edge detection method to find the knee). The ratio of the flux computed with the
spectrally “pure” temperature spectrum to the flux computed with the degraded temperature spectrum is the
q_cfactor that is then applied to water vapor. For CO2 flux, there is very little degradation seen compared to
temperature flux outside of the range of noise, so we instead rely on a mechanically based transfer function
(Lenschow and Raupach, 1991) that describes fluid flow in a tube (function of tube length, radius and Reynolds
number of flow). The temperature spectrum is then degraded using this equation, and the c_cfactor factor is
found as for H2O. Please see Berger et al 2001 for more details.
Step 7. Compute fluxes using detrended, lagged time series and multiply by spectral correction factor. Convert
fluxes to standard units by multiplying by air density or latent heat of vaporization, etc…
> > 3.
A brief description of the tower, and direction of the boom
> > (anemometer),
37 m tower, sonic is on 1 m boom, oriented 228 degrees from true north and mounted at approximately 36 m.
Location of tower: 46.242017 N, 89.347650 W
> > 4.
> > 6.
Height of instruments and distance from tower to shed (or IRGA),
Diameter and length of your tubing
IRGA for flux is LI-6262 located at tower top (36 m). 3.3 m of Teflon tubing connects the sample inlet (near
sonic) to the IRGA sample in. In-between are 5 Millipore 1 um filters arranged in series and parallel. Tube
radius is 0.0019812 m. Sample air is drawn through IRGA, passes a buffer volume and into 9 l/min diaphragm
pump (KNF UN89). Reference gas is dry nitrogen (further dried with drierite and Mg Perc, and CO2 removed
with soda lime) located in shed, at bottom of tower and about 30 m from tower base, connected by ¼” OD
Synflex (aka Dekaron) tubing, sent out at 3.5 psi, 10 ml/min.
Other instruments at tower top: PRT temperature, humidity, direct and total PAR, net radiation, leaf wetness,
and air pressure.
> > 5.
Do you apply the Schotanus equations for sensible heat, or any
> > other conversions to sonic temperature? and
The file I give you reports corrected heat flux. First I take the mean 30 minute mean sonic temperature and 30
minute H2O mixing ratio (from humidity sensor or Licor) and compute air temperature = Tv * (1 –
(mixr/(mixr+eps)) * (1-eps)) where mixr is water vapor dry air mixing ratio in g/g, eps is 0.622, Tv is virtual
temp in degrees K.
Next I convert the Virtual temperature flux in K * m/s into temperature flux using this equation:
Tflx = Tv*(1-eps)*(2*mixr/eps^2.*qflux - qflux/eps) + tvflx*(1. - mixr/eps*(1-eps))
Where Tv is virtual temperature in degrees K. Tvflx is virtual temperature flux in K * m/s, eps is 0.622, mixr is
water vapor dry air mixing ratio in g/g, qflux is water vapor flux in g/g * m/s. I think this is the Schotanus
equation, but I’m not 100% sure. It corrects the flux for both the effect of water vapor and water vapor flux.
Finally, I convert to W/m2
Tflux = (cpd * qrho + cpq * qrho) * tflx
Where drho is dry air density (k/m3) computed from air pressure, mixing ratio and air temperature, and qrho is
water vapor density (kg/m3), cpd is 1004 and cpq is 1952.
(Similar conversions are used to convert water vapor flux to latent heat flux, u* to momemtum flux, and CO2 to
umol/m2/s) – if you want these equations let me know.