INSTRUCTION MANUAL Eddy Covariance System CA27 and KH20 Revision: 7/98 C o p y r i g h t ( c ) 1 9 9 4 - 1 9 9 8 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The CA27 AND KH20 are warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
EDDY COVARIANCE SYSTEM TABLE OF CONTENTS PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. PAGE 1. 1.1 1.2 1.3 2. 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 SYSTEM OVERVIEW Review of Theory ....................................................................................................................1-1 System Description ........................................................................................
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SECTION 1. SYSTEM OVERVIEW 1.1 REVIEW OF THEORY The surface layer (Figure 1.1-1) is comprised of approximately the lower 10% of the atmospheric boundary layer (ABL). The fluxes of water vapor and heat within this layer are nearly constant with height when the following criteria are met: the surface has approximate horizontal homogeneity; and the relationship z/h << 1 << z/zom is true, where zsfc is the height of the surface layer, h is the height of the ABL, and zom is the roughness length of momentum.
SECTION 1. SYSTEM OVERVIEW Wind direction must also be measured. The wind direction is used to identify periods when the mean wind was blowing over the back of the eddy covariance sensors. Flux data from these periods should not be used because of potential flow distortions caused by the body and mounts of the CA27 and KH20. A 75 degree sector behind the sonic and hygrometer exists where flow distortions may occur. TABLE 1.2-1.
SECTION 1. SYSTEM OVERVIEW 1.3.3 NO ABSOLUTE REFERENCE The CA27 zero offset drifts with ambient air temperature. The zero offset drift does not effect the flux measurements, since only the fluctuation about some mean are of interest. This drift does, however, preclude the measurement of the mean vertical wind speed. The 127 does not measure absolute temperature, instead the 127 is referenced to the unknown temperature of the sonic base.
SECTION 2. STATION INSTALLATION Figure 2-1 depicts a typical eddy covariance station that measures the latent and sensible heat flux, ambient air temperature and humidity, wind speed and direction, net radiation, soil heat flux, and soil temperature. Point the eddy covariance sensors into the prevailing wind and the net radiometer to the south. The net radiometer must be mounted far enough from any obstructions so that it is never shaded.
SECTION 2. STATION INSTALLATION 2.1 SENSOR HEIGHT The eddy covariance sensors must be mounted at some height that ensures that the measurements are being made within the local surface layer. The local surface layer grows at a rate of approximately 1 vertical meter per 100 horizontal meters. Thus, a height to fetch (horizontal distance traveled) ratio of 1:100 can be used as a rough rule of thumb for determining the measurement height.
SECTION 2. STATION INSTALLATION FIGURE 2.2-2 CA27, KH20, HMP35C, and Wind Sentry Set On a CM6 Tripod 2.3 KH20 CALIBRATIONS Each KH20 is calibrated over three different vapor ranges. The vapor ranges are summarized in Table 2.3-1. This calibration may have been done under the following conditions: windows scaled and clean, and at sea level or 4500 ft (Logan, UT, 1372 m). TABLE 2.3-1. KH20 Vapor Ranges Range Full Dry Wet m-3 g 2 - 19 2 - 9.5 8.
SECTION 2. STATION INSTALLATION where ρv is the vapor density (g m-3), Rv is the gas constant for water vapor (461.5 J K-1 kg-1) (Stull, 1988). TABLE 2.4-1 Polynomial Coefficients a0 = 6984.505294 a1 = -188.9039310 a2 = 2.133357675 a3 = -1.288580973 x 10-2 a4 = 4.393587233 x 10-5 a5 = -8.023923082 x 10-8 a6 = 6.136820929 x 10-11 2.5 SOIL THERMOCOUPLES, HEAT FLUX PLATES, AND CS615 The soil thermocouples, heat flux plates, and the water content reflectometer are typically installed as in Figure 2.5-1.
SECTION 2. STATION INSTALLATION The sensors are installed in the undisturbed face of the hole. Measure the sensor depths from the top of the hole. Make a horizontal cut, with a knife, into the undisturbed face of the hole and insert the heat flux plates into the horizontal cut. Press the stainless steel tubes of the TCAVs above the heat flux plates as shown in Figure 2.5-1. Be sure to insert the tube horizontally. When removing the thermocouples, grip the tubing, not the thermocouple wire.
SECTION 2. STATION INSTALLATION TABLE 2.6-1. CA27 and KH20 Sensor Lead Color Assignments Sensor CA27 Wind + CA27 Wind CA27 Shield CA27 Temperature + CA27 Temperature CA27 +12 V CA27 Power Gnd KH20 Water Vapor + KH20 Water Vapor KH20 Shield KH20 +12 V KH20 Power Gnd Color Green Black Clear White Black (same as Wind-) Red Black of Red and Black White Black Clear Red Black of Red and Black Tables 2.6-2 and 2.7-1 list the connections to the 21X for the example program in Section 3.
SECTION 2. STATION INSTALLATION Be sure the 21X has a good earth ground, to protect against primary and secondary lightning strikes. The purpose of an earth ground is to minimize damage to the system by providing a low resistance path around the system to a point of low potential. Campbell Scientific recommends that all dataloggers in the field be earth grounded. All components of the system (datalogger, sensors, external power supplies, mounts, housing, etc.
SECTION 3. SAMPLE 21X PROGRAM This section provides a sample program that may be used to measure the eddy covariance sensors and the auxiliary sensors. The CA27, 127, and KH20 are measured in Table 1 at 5 Hz. The meteorological sensors and the energy balance sensors are measured in Table 2 at 0.5 Hz. The meteorological sensors include wind speed, wind direction, air temperature, and vapor pressure.
SECTION 3. SAMPLE 21X PROGRAM ; 05: Z=X (P31) 1: 3 2: 4 ;Copy KH20 output. ; 06: Z=X (P31) 1: 3 2: 5 07: Z=LN(X) (P40) 1: 3 2: 3 X Loc [ lnVh Z Loc [ Vh ] ] X Loc [ lnVh ] Z Loc [ Vh_mV ] X Loc [ lnVh Z Loc [ lnVh ] ] ;Subtract a constant. ; 08: Z=X-Y (P35) 1: 3 2: 23 3: 3 X Loc [ lnVh Y Loc [ lnVho Z Loc [ lnVh ] ] ] ;Subtract a constant. ; 09: Z=X-Y (P35) 1: 4 2: 24 3: 4 X Loc [ Vh Y Loc [ Vho Z Loc [ Vh ] ] ] ;Set Flag 1 high while cleaning KH20 windows.
SECTION 3. SAMPLE 21X PROGRAM 13: If Flag/Port (P91) 1: 10 Do if Output Flag is High (Flag 0) 2: 30 Then Do ;(w'T')rhoCp = H ; 14: Z=X*Y (P36) 1: 18 2: 27 3: 18 X Loc [ H ] Y Loc [ rhoCp ] Z Loc [ H ] ;[w'(lnVh)']Lv/-xkw = LE ; 15: Z=X/Y (P38) 1: 19 X Loc [ LE ] 2: 26 Y Loc [ neg_xkw ] 3: 19 Z Loc [ LE ] 16: Z=X*Y (P36) 1: 19 2: 28 3: 19 X Loc [ LE Y Loc [ Lv Z Loc [ LE ] ] ] ;Add constant to average.
SECTION 3. SAMPLE 21X PROGRAM 23: Set Active Storage Area (P80) 1: 1 Final Storage 2: 12 Array ID 24: Resolution (P78) 1: 0 low resolution 25: Real Time (P77) 1: 0110 Day,Hour/Minute 26: Resolution (P78) 1: 1 high resolution 27: Sample (P70) 1: 4 2: 25 Reps Loc [ neg_kw Sample (P70) 1: 10 2: 10 Reps Loc [ avg_w Sample (P70) 1: 1 2: 21 Reps Loc [ T_lnVh_ ] 28: 29: 30: ] ] Serial Out (P96) 1: 30 SM192/SM716/CSM1 *Table 2 Program 01: 2.
SECTION 3. SAMPLE 21X PROGRAM 05: 06: Z=X*Y (P36) 1: 42 2: 48 3: 42 X Loc [ e ] Y Loc [ RH_frac ] Z Loc [ e ] Volts (SE) (P1) 1: 2 2: 2 3: 11 4: 43 5: 1 6: 0 Reps 15 mV Slow Range In Chan Loc [ SHF#1 ] Mult Offset ;Enter multiplier for SHF#1 (mult#1). ; 07: Z=X*F (P37) 1: 43 X Loc [ SHF#1 F 2: mult#1 3: 43 Z Loc [ SHF#1 ] ] ;Enter multiplier for SHF#2 (mult#2).
SECTION 3. SAMPLE 21X PROGRAM 15: 16: 17: Pulse (P3) 1: 1 2: 1 3: 21 4: 49 5: .75 6: .2 Reps Pulse Input Chan Low Level AC, Output Hz Loc [ WndSpd ] Mult Offset IF (X<=>F) (P89) 1: 49 2: 1 3: .
SECTION 3. SAMPLE 21X PROGRAM 24: Do (P86) 1: 42 Set Port 2 High ;Measure CS615 soil moisture probe. ;When the CS615 is off (Flag 4 low), ;Input Locations CS615_ms and soil_wtr ;will not change. ; 25: Pulse (P3) 1: 1 Reps 2: 2 Pulse Input Channel 3: 21 Low Level AC, Output Hz 4: 52 Loc [ CS615_ms ] 5: .001 Mult 6: 0 Offset 26: 27: 28: Z=1/X (P42) 1: 52 2: 52 X Loc [ CS615_ms ] Z Loc [ CS615_ms ] Polynomial (P55) 1: 1 2: 52 3: 53 4: -.187 5: .037 6: .
SECTION 3. SAMPLE 21X PROGRAM 35: Average (P71) 1: 1 2: 46 Reps Loc [ Tsoil ] 36: If Flag/Port (P91) 1: 10 Do if Output Flag is High (Flag 0) 2: 30 Then Do 37: Z=X-Y (P35) 1: 46 2: 51 3: 47 X Loc [ Tsoil ] Y Loc [ Prev_Ts ] Z Loc [ del_Tsoil ] Z=X (P31) 1: 46 2: 51 X Loc [ Tsoil ] Z Loc [ Prev_Ts ] 38: ;Apply temperature correction to soil ;moisture data measured by the CS615.
SECTION 3.
SECTION 3. SAMPLE 21X PROGRAM 05: 06: Z=F (P30) 1: 1010 2: 27 F Z Loc [ rhoCp Z=F (P30) 1: 2440 2: 28 F Z Loc [ Lv ] ] ;Measure constant for first pass. ; 07: Volt (Diff) (P2) 1: 1 Reps 2: 15 5000 mV Fast Range 3: 3 In Chan 4: 24 Loc [ Vho ] 5: 1 Mult 6: 0 Offset ;Constant for first pass.
SECTION 3. SAMPLE 21X PROGRAM 19: Internal Temperature (P17) 1: 40 Loc [ RefTemp ] ;Prev_Ts for first pass. ; 20: Thermocouple Temp (DIFF) (P14) 1: 1 Reps 2: 1 5 mV Slow Range 3: 4 In Chan 4: 2 Type E (Chromel-Constantan) 5: 40 Ref Temp Loc [ RefTemp ] 6: 51 Loc [ Prev_Ts ] 7: 1 Mult 8: 0 Offset 21: End (P95) 22: Beginning of Subroutine (P85) 1: 4 Subroutine 4 23: Z=X*F (P37) 1: 49 2: .2 3: 37 X Loc [ WndSpd F Z Loc [ C ] Z=X*F (P37) 1: 37 2: .
SECTION 3. SAMPLE 21X PROGRAM 30: End (P95) 31: Beginning of Subroutine (P85) 1: 5 Subroutine 5 32: Z=X*F (P37) 1: 49 X Loc [ WndSpd 2: .00174 F 3: 35 Z Loc [ A ] 33: Z=X+F (P34) 1: 35 X Loc [ A ] 2: .99755 F 3: 38 Z Loc [ CorrFact ] ;Enter the negative multiplier (n.nnn). ; 34: Z=X*F (P37) 1: 45 X Loc [ Rnet n.
SECTION 3. SAMPLE 21X PROGRAM TABLE 3.1-1.
SECTION 4. CALCULATING FLUXES USING SPLIT SPLIT (PC208E software) can be used to apply the air density and oxygen corrections to the measured surface fluxes. This section provides example SPLIT programs to make the necessary calculations on the data produced by the sample datalogger program. All the calculations in ECRAW.PAR and ECFLUX.PAR are explained in Sections 1 and Appendix A. Two runs through SPLIT are required to combine the data and then apply the corrections.
SECTION 4. CALCULATING FLUXES USING SPLIT column # 7: column # 8: column # 9: column # 10: column # 11: column # 12: column # 13: column # 14: column # 15: column # 16: column # 17: column # 18: HEADINGS for , col. # 19: column # 20: column # 21: column # 22: column # 23: column # 24: column # 25: column # 26: column # 27: column # 28: column # 29: Lv old avg w avg T avg InV avg Vh std w std T std InV std Vh H LE T′InV′ Tair e Rn F S ws wd sd wd Lv new Cp rho air TABLE 4.2-2.
SECTION 5. TROUBLESHOOTING This section offers some solutions to common problems. All the locations and data values are based on the example program in Section 3. 5.1 SYMPTOMS, PROBLEMS, AND SOLUTIONS 1. Symptom: The temperature is a constant value of 17, with the fractional portion randomly fluctuating. Problem: The 127 fine wire thermocouple is broken or not installed. Solution: Replace or install the 127. 2. Symptom: Signal response on the 127 is down. Input location 2 data is fluctuating slowly.
APPENDIX A. USING A KRYPTON HYGROMETER TO MAKE WATER VAPOR MEASUREMENTS A.1 WATER VAPOR FLUXES The krypton lamp used in the hygrometer emits a major line at 123.58 nm (line 1) and a minor line at 116.49 nm (line 2). Both of these wavelengths are absorbed by water vapor and oxygen. The equation below describes the hygrometer signal in terms of absorption of both lines by water vapor and oxygen.
APPENDIX A. KRYPTON HYGROMETER IN WATER VAPOR MEASUREMENTS LE = L v )′ ( w ′ InVh − xk w + OC1 (9) A.2 VARIANCE OF WATER VAPOR DENSITY Where OC1 is defined by Eq. (10). ( ) k o C oMoP −1 ′ OC1 = L v w′ T −k w R (10) It would be more convenient if the oxygen correction could be written in terms of the covariance of the vertical wind speed and temperature instead of the inverse of temperature. With that in mind, Eq. (6) can be rewritten to take on the following form.
APPENDIX A. KRYPTON HYGROMETER IN WATER VAPOR MEASUREMENTS where T is in Kelvin. Directly substitute Eq. (19) into (16) and ignore the last term with order T −4 . This yields Eq. (20). ( ρ′v ) 2 = ′ 2 InVh ( ) ( − xk w ) 2 + OC VAR (20) where OCVAR is defined by Eq. (21). OC VAR 2C oM oP = − RT 2 ko x −k w ( )2 ′ ′ T InVh (21) ( ) To find the standard deviation of water vapor, simply take the square root of Eq. (20).
APPENDIX B. REMOVING THE TRANSDUCERS ON THE CA27 Firmly hold the transducer, while loosening the knurled knob. Once the knob is loosened, gently pull the transducer from the arm (see Figure B-1). FIGURE B-1.
APPENDIX C. ADJUSTING THE CA27 ZERO OFFSET A zero velocity anechoic chamber can be made by lining a 5-gallon bucket with foam. The foam lining prevents acoustical reflections from the bucket walls. Two small dish cloths can be used to close off the opening of the bucket. Place the CA27 head inside the foam-lined bucket. Cover the opening with the dish cloths. Connect the CA27 to the electronics box and the Signal/Power cable to the appropriate channels on the datalogger.
APPENDIX D.
APPENDIX E. REFERENCES Brutsaert, W.: 1982, Evaporation into the Atmosphere, D. Reidel Publishing Co., Dordrecht, Holland, 300. Buck, A. L.: 1976, “The Variable-Path LymanAlpha Hygrometer and its Operating Characteristics," Bull. Amer. Meteorol. Soc., 57, 1113-1118. Campbell, G. S., and Tanner, B. D.: 1985, “A Krypton Hygrometer for Measurement of Atmospheric Water Vapor Concentration." Moisture and Humidity, ISA, Research Triangle Park, North Carolina. Dyer, A. J. and Pruitt, W. O.
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