Manual Installation, Operation and Maintenance of Buoy Operated Automatic Meteorological Stations Established in Lake Nasser Entebbe August 2001 Information Products for Nile Basin Water Resources Management www.fao.
The designations employed and the presentation of material throughout this book do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization (FAO) concerning the legal or development status of any country, territory, city, or area or of its authorities, or concerning the delimitations of its frontiers or boundaries.
List of Acronyms List of Acronyms AH AWS CHG CSi DoD DSP FAO FSA G HADA ID LVBD METSTAT NBD OCV P PV RAM RH SM4M SoC SPTR SVP VP VPD Ampere Hour Automatic Weather Station Charge Campbell Scientific Depth of Discharge Data Storage Pointer Food an Agriculture Organization of the United Nations Final Storage Area Ground Terminal High Aswan Dam Authority Identification Code Lake Victoria Basin Database Meteorological Station Datalogger Programme Nile Basin Datab
Table of Contents Table of Contents 1 Introduction 9 1.1 General 9 1.2 Individual Components of the Met Station 9 1.3 Overview of the Contents of the Manual 12 2 CR10X Storage and Control Module 13 2.1 General 13 2.2 Installation 14 2.3 Use 18 2.4 Maintenance 19 2.5 Signature 20 2.6 Prompt Sheet 20 2.7 Trouble Shooting 20 3 Sensors 23 3.1 RM Young 05103-L Wind Monitor 23 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.2 Q-7.1-L REBS Net Radiometer 3.2.1 3.2.2 3.2.3 3.2.4 3.
Table of Contents 3.4 Model 108 Temperature Probe 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 3.5 General Installation Use Maintenance Trouble Shooting KVH C100 Compass Engine (SE-25 Sensor) 3.5.1 3.5.2 3.5.3 3.5.4 30 32 General Installation Use Maintenance 4 Power Supply 34 4.1 General 34 4.2 Sealed Rechargeable Battery 34 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.3 Solar Panel 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5 4.
List of Figures List of Figures Figure 1: Figure 2: Figure 3: Figure 4: Figure 5: Figure 6: Figure 7: Figure 8: Figure 9: Figure 10: Figure 11: Figure 12: Figure 13: Figure 14: Figure 15: 6 Sketch of an Automatic Met Station Installed on Buoy CR10X Datalogger and Control Module Power Supply BP24 and CH12 Charger/Regulator Portable Keyboard Display CR10KD and Data Storage Module SM4M The Wiring Panel Power Supply and CR10X in Protective Enclosure RM Young Wind Monitor
List of Tables and Boxes List of Tables Table 1: Table 2: Wiring Schedule SoC Versus Open Circuit Voltage for Yuasa 7 Ahr Lead Acid Gel Battery 16 36 List of Boxes Box 1: Box 2: Box 3: Box 4: Box 5: Box 6: Box 7: Box 8: Permanent Storage of BUOY_METSTAT in Program Location 7 & 8 of the SM4M Loading BUOY_METSTAT into CR10X Storage and Control Module Temporarily De-activate Security Transfer Data Prior to Re-loading BUOY_METSTAT into CR10X Deter
Annexes Annexes Annex 1: Annex 2: Annex 3: Annex 4: ings Annex 5: Annex 6: Annex 7: Annex 8: Annex 9: 8 Installation and Operation of PCTour Wiring Diagram for CR10X Using BUOY_METSTAT Input Storage Locations Used by BUOY_METSTAT Guidelines for Assessing Station Performance Using Daily Signature and Battery Voltage RecordBattery Log Book Specimen Guidelines for Loading BUOY_METSTAT into Program Location 7 & 8 of SM4M Storage Module Wind Vector Sample Calculation of Open Water Evaporation Using Priestley-
Introduction Introduction 1.1 General This manual presents detailed instructions for the installation, operation, and maintenance of the Automatic Weather Stations (AWS) installed on buoys in Lake Nasser in Egypt by the FAO Nile Basin Water Resources Project. The monitoring equipment was procured from Campbell Scientific, USA. This company has a proven track record in Africa, and a number of Campbell Scientific AWS have been operational in the basin for several years.
Introduction Temperature & RH Sensor Wind Monitor at 4m Cross Arm Solar Panels Lantern Super Structure Temperature & RH Probe Wind Monitor at 2m Net Radiometer Instrument Container Buoy Hull Water Temp Sensor Lighting Rod Figure 1: Sketch of an Automatic Meteorological Station Installed on Buoy The main components of the Met Station are: • • • • • • • • • • Buoy hull (imported) The instrument tower (super structure manufactured locally) 019ALU cross arms installed on the instrument tower Instrument con
Introduction .111, L.- ..... - -- . . . - L714-...304-101,..)1-10j Figure 2: CR10X datalogger and control module Figure 3 presents the BP24 rechargeable battery and the CH12R regulator and charging unit. Yuasa Rechargeable Battery Regulator / Charger AZAUY117 vsr 0101: LIZALIRA1310 rIAAS 11,11-11.11 TO7ITAA :-°(7,0%, fQ)cSr Mutt 47 DST 1113.115.P4 JED A.C11 . wow a Wow.. vs on...w. Lnrormoar=orw= .A2AUY r 1,41.4 MD KAI .01 .1421 .
Introduction Figure 4 presents the portable keyboard display and the data storage module, which are used together to communicate with the data logger while in the field. One set can serve several stations, as these items are only used during the periodic inspection visits. The storage module is a solid, rugged instrument, and is used to transfer the measurement values from the datalogger in the field to a PC in the office.
CR10X Storage and Control Module CR10X Storage and Control Module 2.1 General The CR10X is the actual datalogger. It is an electronic storage and control system that manages the data acquisition, processing, storage, and retrieval within the Met Station. The CR10X hardware consists of (a) a measurement and control module, and (b) a detachable wiring panel.
CR10X Storage and Control Module The datalogger has two separate memories, i.e.: (1) a Flash ROM of 128 Kb for storing the operating system and various datalogger programs, and (2) a RAM of 2 MB for data processing and storage. The CR10X datalogger has no internal power supply, apart from a small lithium battery for back-up purposes. Instead, the logger draws its electricity from the external BP24 power unit with CH12R charger, connected to a solar panel. This unit is discussed in detail in chapter 4.
CR10X Storage and Control Module Figure 6: Power Supply and CR10X in Protective Enclosure Fix the central grounding cable of the protective enclosure to the ground terminal on the CR10X wiring panel. This is essential for protecting the instrument against lightning strikes. It is also crucial for obtaining precise measurements, as sensors and datalogger need the same ground reference.
CR10X Storage and Control Module Table 1: Wiring Schedule No Sensor 1 HMP45C-2M (Temp & RH) Sensor (1) at 2 Meters 2 HMP45C-4M (Temp & RH) Sensor (2) at 4 Meters 3 Q-7.
Note: BUOY_METSTAT1 is a datalogger program with datalogger identification No. 1 for Kalabshah Khor while BUOY_METSTAT2 is the datalogger program with datalogger identification No. 2 for Toshka Khor. The basic program for the both dataloggers is the same with the only difference that different datalogger identification numbers are embedded in the program. This ID serves to separate data from different sources.
CR10X Storage and Control Module “DDDD” (enter Julian Day; See Prompt Sheet to transfer calendar days to Julian days) “A” (keyboard equivalent to ENTER) “HHMM” (hour and minute) “A” (keyboard equivalent to ENTER) The last step in the installation process is protecting the system against unauthorized user interventions. For this purpose a password is introduced, which blocks access to (a) modifying the active datalogger program, (b) loading new programs, and (c) changing the memory allocations.
CR10X Storage and Control Module connected to the datalogger, which is of course the dominant situation, BUOY_METSTAT simply aborts instruction 96 and continues with the next line in the program. Hence downloading data from the CR10X datalogger to the SM4M storage module is accomplished by simply connecting the SM4M to the logger for minimal five minutes. However, to be positively sure that all data have been transferred, it is advised to keep the storage module connected for at least 15 minutes.
CR10X Storage and Control Module The CR10X contains an internal lithium coil cell battery that operates the internal clock and SRAM when the datalogger is not connected to an external power source. This lithium battery should last for at least 4 years when no external power is available. However, in the default situation the datalogger is connected to the BP24 power supply, and the expected lifetime of the lithium battery is therefore around 10 years.
CR10X Storage and Control Module Box 4: Transfer Data Prior to Re-loading BUOY_METSTAT into CR10X Although re-installing BUOY_METSTAT does not erase information stored in the logger’s Final Storage Areas, it is advised to transfer all data to the storage module prior to (re-) loading BUOY_METSTAT into the CR10X. To this effect, follow the instructions given in paragraph 2.3.
CR10X Storage and Control Module Software. The user is referred to the separate SPLIT manual, included in Campbell Scientific’ Instruction Manual for the PC208W Datalogger Support Software. Problem 3: Although data transfer from logger to SM4M has been concluded successfully, the downloaded data does not cover the whole period between present and previous data dump. Instead, the available data only seems to come from the most recent period.
Sensors Sensors 3.1 RM YOUNG 05103-L Wind Monitor 3.1.1 General The Met Station includes the RM Young Wind Monitor with integrated anemometer propeller and wind vane for measuring horizontal wind speed and wind direction. This model is originally developed for ocean data installed on buoy platforms. It is rugged and corrosion resistant. Wind observations are mainly used for determining potential evaporation.
Sensors 3.1.2 Installation The wind sensors should be located away from wind obstructing obstacles like trees and buildings. As a general rule, the horizontal distance between wind set and obstruction should measure at least ten times the height of the obstruction. Follow the below instructions to install the Wind Set at 2 meters height and 4 meters height. Figure 7 presents a graphic explanation of the sensor.
Sensors needle points to magnetic north 3 degrees, 0 minutes west true north Figure 8: Declination Angle in the Lake Victoria Region 3.1.3 Operation Operation of the RM Young Wind Monitor is fully automatic and does not require any user intervention. The appropriate instructions for this purpose are included in the datalogger program BUOY_METSTAT. 3.1.
Sensors Annex 3, which one is used for Wind Direction and use the “A” key to advance to this location. Manually rotate the wind vane to its maximum location; this is where the value on the keyboard jumps back to zero. Write down the maximum wind direction (e.g. 367 degrees). Adjust the multiplier in the Wind Direction Instruction in BUOY_METSTAT by multiplying this value with 360 divided by the maximum wind direction.
Sensors Support Arm Level Bubble Thermopile Sensor (inside) Figure 9: Q-7¬.1-L REBS Radiometer The operation of the Net Radiometer is fully automatic and no user actions are required. The appropriate instructions to this end are included in the BUOY_METSTAT datalogger program. 3.2.3 Maintenance The following maintenance is required: • During every visit to the Met Station, inspect the silica gel to ensure it is still blue and white.
Sensors and distilled water. • If condensation inside the wind shields still persists, remove the wind shields as described below: 1. 2. 3. remove the mounting screws and the clamping rings allow the condensation to escape or to evaporate for 15 minutes. replace the wind shields while making sure that the O-rings are in their grooves before clamping the windshields into place. gently tighten the screws in the following sequence: first, third, fifth, second, forth, sixth.
Sensors For detailed specifications, the reader is referred to corresponding Campbell Scientific Instruction Manual for the HMP45C Temperature and Relative Humidity Probe. 3.3.2 Installation The HMP45C temperature and relative humidity sensor is installed at 2 meters and 4 meters height on the instrument tower. It must be housed inside a solar radiation shield while used in the field. Clamp the radiation shield to the tripod mast as shown in figure 10.
Sensors 3.3.3 Use The operation of the HMP45C is fully automatic and no user action is required. The appropriate operating instructions are included in the BUOY_METSTAT datalogger program. 3.3.4 Maintenance The HMP45C requires minimal maintenance, as follows: • • During each visit to the Met Station, check if the radiation shield is free from dust and debris; Each two years, replace the humidity chip (contact Campbell Scientific). 3.3.
Sensors Figure 11: Model 108 Temperature Sensor Attach the sensor cable to the wiring panel of the CR10X datalogger according to the wiring diagram in table 1 in paragraph 2.2, and Annex 2, as follows: 108 Temperature Sensor (1) at 0 Meters Depth: Clear wire to terminal G Purple wire to terminal AG Black wire to terminal E1 Red wire to terminal H4 108 Temperature Sensor (2) at 20 Meters Depth: Clear wire to terminal G Purple wire to terminal AG Black wire to terminal E1 Red wire to terminal L4 3.4.
Sensors 3.5 KVH C100 Compass Engine (SE-25 Sensor) 3.5.1 General The automatic buoy meteorological stations contain two wind monitors for measuring wind speed and wind direction installed at 2 meters and 4 meters height. However, as obvious from its name, the buoy stations are subject to pitch and roll movement whereby the wind monitor cannot measure the right wind direction. To correct the wind direction error, the compass sensor is used in combination with the wind monitor sensors.
Sensors 3.5.3 Use The operation of the C100 compass engine is fully automatic and no user action is required. The appropriate operating instructions are included in the BUOY_METSTAT datalogger program. 3.5.4 Maintenance The C100 compass engine is protected in a weatherproof tough housing from the factory. Therefore it does not require any maintenance.
Power Supply Power Supply 4.1 General The Met Station is equipped with electronic sensors and an electronic datalogger. Hence electronics play an important role in the data acquisition process. Proper performance of electronic equipment depends to a large extent on a stable and reliable power supply. Failure of electronic equipment is all too often the result of power surges, power cuts, and related spikes. The above clearly indicates the crucial role of the power supply in the Met Station.
Power Supply 4.2.2 Installing/Changing the Battery The BP24 power supply consists of a housing for and 24 AH battery. It is shown on figure 13, together with other elements of the power supply.
Power Supply 4.2.3 State of the Battery To avoid either deep discharge or overcharge, the amount of energy in the battery needs to be monitored. The State of Charge (SoC) is a good indicator for this. Table 2 presents the SoC for the Yuasa 24AH sealed lead-acid battery as function of the voltage, for a situation when no load is attached. This is called the Open Circuit Voltage (OCV).
Power Supply Figure 14: Constructed State of Charge (SoC) versus Open Circuit Voltage (OCV) Given 12.9 V at SoC 100% Given this individual SoC-OCV relation, the user can now assess the SoC of a known lead acid battery.
Power Supply Overcharging a sealed (captive) electrolyte battery will cause loss of electrolyte and will strongly reduce battery life. Moreover, overcharging may lead to the formation of dangerous levels of highly explosive hydrogen gas. Likewise, fast charging greatly reduces the life of the battery by quickly lowering the level of electrolyte in the cells, herewith damaging the plates. The user is therefore advised to only recharge the battery using the provided CH12R charger.
Power Supply • 4.3 Regularly grease the terminals and contacts to avoid corrosion. Solar Panel 4.3.1 General The solar panel is a photovoltaic (PV) power source used for charging the sealed lead-acid battery of the Met Station. It therefore constitutes the primary energy source of the system, although it does not directly power the datalogger and sensors. The MSX10 solar panel itself does not include a regulator.
Power Supply Figure 15: Mounting of the Solar Panel on the Mast 4.3.4 Maintenance The MSX10 Solar Panel requires a minimum of routine maintenance. The following is recommended: • • • • To improve the panel’s efficiency, clean the glass plate during each visit with a soft, lightly moistened cloth. Do not use any abrasive pad or cleaner, as this may permanently scratch the glass. Please keep in mind that a dust cover on top of the module is reducing power output.
Power Supply 4.4.3 Use Operation of the charging unit/regulator is almost completely automatic. User intervention is limited to toggling the power to the datalogger On/Off. A red light (LED) indicates when a charging source is connected to the charging unit/regulator. 4.4.4 Maintenance Apart from checking periodically if all contacts are firmly connected and not corroded, no maintenance is necessary. 4.5 Grounding 4.5.
Buoys and the Instrument Tower Buoys and the Instrument Tower 5.1 General All the meteorological sensors and related equipment are installed on buoys in Lake Nasser. The buoys are partly manufactured from Ocean Science, USA and partly by High Aswan Dam Authority (HADA).
Annexes Annexes Annex 1: Installation and Operation Instructions for PCTour 1. General PCTour is a DOS based software package provided by Campbell Scientific. It concerns a computer based guided tutorial that presents basic concepts of CR10X and software operations. For example, the functions of the I/O channels are discussed, as well as the concepts of Input, Intermediate, and Final Storage. PCTour also briefly discusses PC208 software, including a discussion on EDLOG and SPLIT.
Annexes Annex 2: G G H1 L1 AG H2 L2 AG H3 L3 AG E1 AG E2 G P1 G P2 G C8 C7 C6 C5 C4 C3 C2 C1 G 12V 12V HMP45C (1): HMP45C (2): 05103 (1): 05103 (2): 108W (1): 108W (2): Q-7.1: C100: 44 Wiring Diagram for CR10X Using BUOY_METSTAT Datalogger Program HMP45C (1) clear HMP45C (2) clear 05103 (1) black 05103 (1) clear 05103 (2) black 05103 (2) clear 108W (1) clear Q -7.
Annexes Annex 3: Input Storage Locations Used by BUOY_METSTAT Connect keyboard display to datalogger and use “*6” Mode to view the input storage locations. Press “A” to proceed from one variable to another.
Annexes Annex 4: Guidelines for Assessing Station Performance Using Daily Signature and Battery Voltage Recordings 4-A General BUOY_METSTAT includes routines to monitor two essential station performance indicators, namely (1) battery voltage and (2) the signature of the active datalogger program. The Open Circuit Voltage (OCV) of the battery in use is measured automatically on a daily basis.
Annexes This window is used to select the appropriate data file, containing all Met Station data values for the recording period, and a pre-programmed “parameter” file called HADA_PRF.PAR, which function as to automatically split station performance information from the rest of the station output. To open HADA_PRF.PAR, follow the below instructions: • • • click the “OPEN” instruction of the “FILE” menu navigate to the location which contains the HADA_PRF.PAR file select this file and click “OK”.
Annexes REV litSplit Version 1.7 File Edit Labels Run Printer Help Input File(s) Clirtput File Input Data File Open Browse Start l:ondition File name: Folders: HADA_PRF PAR cAcampbellVilesNparametr oK Offsets I IT.ancel ['HA AWS.PAR c: HAD.4_DAY.PAR Stop Condition CAMPBELL HADA HR.PAR HADA PRF.PAR Pararrietr etday. par Copy METHOUR PAR ME T PE R F. PA R ME T RAI N PA R Select Network... L.
Annexes .... Split - HADA_PRF.PAR File Labels Edit Printer Run Help S./ Input File(s) Output File 'MN Input Data File Select Input File File name: Folders: ID. at.aui_17,dat c:\carrrpbell\liles\iriput IBrowse Start Cordtion Offsets Lance' Dafauljb.dar. Data007.dat [L CAMPBELL Stop Cordtion- Network . Files Input pCo 1[200) List files of t,pe : FS elect Data Drives: I I= c. DATI 2,3,5,6 DATA007.
Annexes After running the HADA_PRF.PAR file in SPLIT with the appropriate data file, the following station information appears on the screen: Split Run 1.7 Buoy Station Performance Year _PITI D ay_RTM Bat_Volt Pro g_S g !Iin 9003 9003 113 114 12.38 12.4 Reading files completed.
Annexes Annex 5: Batterry Log Book Specimen Battery Specifications Number: Main Office: Date of Purchase: Make: Type: Capacity: Battery Log Date Initial Voltage [V] Initial SoC [%] Activity Final Voltage [V] Final SoC [%] Remarks Manual 51
Annexes Annex 6: Guidelines for Loading BUOY_METSTAT Datalogger Program into Program Location 7 & 8 of the SM4M Storage Module 6-A General As discussed in chapter 2, the two datalogger programs need to be stored in program location 7 and 8 of the SM4M storage Module. It is advised to permanently store: 1. “BUOY_METSTAT1” for Khalabshah Khor in program location 7 of the SM4M; and 2. “BUOY_METSTAT2” for Toshka Khor in program location 8 of the SM4M.
Annexes Double click this icon to activate PC208W. The following toolbar appears: Double click the Stg Module icon. In the window that appears, first click the “SM4M/SM16M” tab at the top right most corner of the screen, and subsequently the “Setup” tab at the bottom-left. The following window shows up. III .g?,SMS File Options Data T ools la Help CS tvil .4,11=F1 F't Card IM !E; tvi 1 92/SM 71 SM4M/SM16M: Stet us 8 o x Module Pointers COM Port Setup Free :;pace Storage Ref.
Annexes P Data Options File Help Tools SM192/SM716 GSM-IA/CAI rStatusBox I Module Pointers COM Port Setup Free Space Stnrage Ppf. Pointer Display Pointer DumpPointer Port COM1 r Baud Pate COM2 2086446 10575 2 , 10575 9600 C COM3 COtv14 FE Via 11...RI,L.: AL I SM4M/SA41614! PG Card Target Address c3 C Auto 6- 1 r4 raja& r r r 5 r 1- Module Values Good FLASH blocks Error Count Programs 64 o Switch Settings Ring tvlode Address 1 76800/9600 Baud S tatusAdvanced...
Annexes To load BUOY_METSTAT in program location 7, check the box in front of “Prog 7” and click “Store”. A navigation screen appears as presented below. kJ File Options Data Tools Help CS Ml /1 1R1 SM192/!E;M716 Programs PC card SM4M/S1416M Select program 8 Prograrr r Prog 1_41 pc208,....., Look in: J Bin Prog 2 lnifiles r Prog 3 Ili r Prog 4 r Prog 5 Metstat.
Annexes Annex 7: Wind Vector Wind speed and direction are measured with a polar sensor (R. M. YOUNG 05103). The raw data are processed to a wind vector, which includes: a. b. c. Mean horizontal wind speed, S [m/s] Unit vector wind direction, 1 [degrees] Standard deviation of wind direction, (1) [degrees] Mean horizontal wind speed is calculated using: S = (Si)/N In which the indices i denotes each individual sample.
Annexes Annex 8: Sample Calculation of Open Water Evaporation Using Priestley-Taylor 1. Introduction 2. The Energy Balance Method This document presents a sample calculation of open water evaporation of a large water body in an arid zone using Priestley-Taylor (PT). The sole aim of this exercise is to demonstrate the methodology. The values of the variables used in the calculation are fictitious and do not represent actual measurements.
Annexes = gradient of the saturated vapor pressure versus temperature curve y = psychrometric constant (function of air temperature and barometric pressure) Rn = net solar radiation ES = change in energy storage in the water body The semi-empirical coefficient a varies per climate zone. In humid areas, research supports a value of 1.26 for a free water surface, while for arid locations a value of 1.74 was found more appropriate.
Annexes 3.3 Right-Hand Terms of the Priestley-Taylor Equation gradient of the saturated vapor pressure The saturated vapor pressure is a function of the air temperature. It is expressed by the following equation: esat = 0.611 exp( 17.3 Ta / (Ta + 237.
Annexes However, in line with its name, the psychrometric constant y is virtually constant, with a typical value of 0.066 [kPa °C-1]. Thus: y = 0.066 [kPa °C-1] Net Solar Radiation Rn Net Solar Radiation is calculated with: Rn = R short-wave-in – R short-wave-out + R long-wave-in – R long-wave-out Short wave radiation has a wavelength between 0.2 and 2 m, while long wave radiation encompasses the spectrum from 4 to 50 m. Incoming and reflected solar radiation is typically measured with a pyranometer.
Annexes ES = cw x w S (DiTi2 – DiTi1) in which: ES cw w Di Ti1 Ti2 = change in energy storage [J] = the specific heat of water [J C-1 g-1] = the mass density of water [g M-3] = height of depth layer i = average temperature of depth layer i at time step 1 = average temperature of depth layer i at time step 2 BOX 3: Calculation of net long-wave radiation for a water body of 20 °C, in an arid region with a surrounding average air temperature of 20 °C, and an average relative humidity of 35%. esat = 0.
Annexes BOX 4: Sample Calculation of ES Table 1 presents the temperature changes in a fictitious water body with a total depth of 20 m with a time step of 1 day. Depth 0 2 5 10 15 20 T2 [°C] 20 19.9 19.9 19.6 19.6 19.5 T1 [°C] 19.9 19.8 19.8 19.6 19.6 19.5 T [°C] 0.1 0.1 0.1 0 0 0 Table 2 presents the average temperature change per depth layer. Layer 0–2 2–5 5 – 10 10 – 15 15 - 20 Layer depth [M] 2 3 5 5 5 Depth x Tavg[°C] 0.1 0.1 0.05 0 0 Tavg[M °C] 0.2 0.3 0.
Annexes in which: E = evaporation rate [M day-1] = is Latent Heat of Vaporization [J g-1] v = mass density of water [g m-3] w = gradient of the saturated vapor pressure versus temperature [kPa °C-1] y = psychrometric constant [kPa °C-1] Rn = net solar radiation [J M-2 day-1] ES = change in energy storage [J M-2 Day-1] Net Solar Radiation Rn Rn = R net-short-wave + R net-long-wave Using the formulas and box-calculations described in the previous text, it follows that: R net-short-wave = R short-wave-in x
Annexes Evaporation Rate E E = (1.74 / v w)x / ( + y) x (Rn - ES) Inserting in this formula the values calculated above, it follows that: E = (1.74 / (2450 * 0.99836 x 106) x 0.145 / (0.145 + 0.066) x (13.27 – 3.13) x106 E = 5.0 x 10-3 [M day-1] Thus, the open water evaporation for this particular situation is estimated at 5.0 mm per day. The reader should note that the specified conditions do not represent the actual Lake Nasser environment and are solely used for demonstration purposes. 5.
Annexes Annex 9: Calculation of Harbeck Evaporation for a Five-Minutes Interval The Harbeck equation, which is an exponent of the Mass-Transfer Approach, is expressed by: E= x va x (es – ea) E va es ea = mass-transfer coefficient = evaporation [cm day-1] = wind speed at 2 m [cm s-1] = vapor pressure at the water surface [mb] = vapor pressure at 2 m [mb] HADA uses the standard value of = 1.26 x 10-4 for the mass-transfer coefficient.
