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1. ao ere lus oboe 6 3 1 3 Calibration Fixture and Plaque i i ee e eto Re na nde nec do enean 6 3 4 dnstrument Setup ee reae trt v Tete 6 3005 UNUS 6 3 3 BASELINE CATPIBRATION rore 7 334 DARK OFFSET MEASUREMENT ee SLOT 7 34L LIUM E E 8 34 2 GOMCCHON 8 3 3 MBASUREMENT 5 9 2254 Preparation oe tete Deck tas ee Navas Ba aes te E eo Een 9 3 3 2 Setting the Channel Gains ea hei eee en es 9 3 5 3 Measuring the Response Curves eene eene 9 3 54L Plaque Reflectivity seed eee be 10 35 3 1 Loading s ios studente t Reli E ede 11 3 6 GAIN RATIO 22 ee 11 3 06 15 cette tapes st pe ecrit UE 11 3 06 27 s ted 12 3 6 3 Setup and Procedure for HydroScat 6P ccccccccccccssssseesceseeseesceseeseeesseeseceseecnseeseesenseeaeeaeeneeas 12 3 6 4 Direction of MOOM hennie en eniti aterert es edet 12 3 6 5 Continuing2. 3 6 5 Continuing Procedure Once you have selected the direction of target motion HydroSoft continu ously monitors the signal levels from the instrument and instructs you when and in which direction to move the target During this process it highlights the numerical signal values with colors to indicate how close they are to their ideal values GREEN highlighting indicates values in the optimum range of 25000 to 30000 When at least one channel is in this range HydroSoft will instruct you to stop the target and when you acknowledge this it will proceed to measure ratios on the eligible channels Eligible channels include those in the range from 10000 to 25000 which are shown with YELLOW highlighting RED indicates a channel is saturated with a value either above 30000 or at 0 In this case HydroSoft will instruct you to move the target in the appropriate direction to reduce the signal WHITE no highlighting indicates a channel is either below 10000 or that it is not presently being considered for measurement regardless of its value This can happen if the channel has already been measured on the current gain or if hard ware limitations prevent it from being measured simultaneously with some other channel If using the dark target procedure described in section 3 6 3 remove the dark target after the 5 4 column is complete as shown in the figure above Other wise the signal levels will not be high enough to measure the lower
3. 1 n e TABLE OF CONTENTS OVERVIEW o eye eov d Vo te ve cn 1 1 12 CORRFICTENTS RAE E A E A 1 1 25 ret tede fette ie ter i 1 1 35 GAIN RATIOS 1 1 4 SEQUENCE OF PROCEDURES cccccccssssceceessececeescecesseccesesueeceessececsseeeceesseeecessseccsssecesesseeceesseeecnseeeees 2 1 5 HYDROSOFT 000 000000000000000000000000000000000 eseese oe 2 1 6 CALIBRATION RESULTS cccccccccssssssscecececeesssecsecceecessuseeececsesssaececeeeeecesaecaeceecceseaeseeeescseseseeeeesesees 2 CALIBRATION FIXTURE ses 55250226064 cosvacsoseesessessnsosconasoacosbeensseeneesvecbeascsnaces cuasouasacsvessascseensecese 3 214 DESCRIPTION 2 5 ies vedo sett 3 222 HANDEE TINSTALEATION ete EEE 3 2 3 CALIBRATIONIPEAQUE 15 6n I ash ne ta rrt seii BR UE 4 2 4 PEAQUE MAINTENANGE eee nem eee tubis edu pv 4 PROCEDURES eo once costa abra Reeves pes bolo ORE RO ERE 6 GENERAL PREPARATION i a aeter e PU ei ve eed 6 B D De SCOMpitek i e eee e A toto ioter etos 6 31 22 Environments n e e e
4. Procedure sni eee eite eel ies 13 3 75 STORING GAUIBRATION 2RESUETS ib ve e o i erste 14 3 8 HINATSS FERS ten sub Ft 14 3 0 7 56 vo et 15 3 9 15 ERU GA a 15 3 90 35 16 COEFFICIENT CALCULATIONS 55 17 AJ mete eder 17 225 SIGMA ero cete ivit ded nA tete alae eee 18 43 DARK OEESEIS eoo terae ute Supe ests PU 19 5 LT 20 iii 1 OVERVIEW HOBI Labs HydroScats HydroScat 2 4 and 6 a Beta c Beta in struments for measuring optical backscattering in natural waters For detailed in formation about these instruments see their individual User s Manuals available from www HOBlILabs com One of their key features is the capability for a rigor ous calibration that is robust enough to be performed by users in their labs or in the field The calibration requires a fixture described in section 2 which can be purchased from HOBI Labs HOBI Labs HydroSoft software versions 2 5 and later guides users thro
5. S 5 is the raw signal from the instrument in digital counts measured when the LED is on Soy 15 the raw signal when the LED is off the signal due to electronic offsets R is the reference measurement of LED output when the LED is on Roy 15 the reference measurement when the LED is off due to electronic offsets is the distance from the instrument face to the calibration plaque N H is the distance between the centers of the source beam and receiver field of view depends on the instrument model pL 18 the radiance reflectivity of the calibration plaque Zmin is the minimum distance to consider in the calibration at very small values of z the only light received is due to multiple reflections be tween the plaque and the instrument face which should not be in cluded in the measurement 17 Zmax 18 the distance beyond which the plaque is invisible to the sensor Note that o differs from the irradiance reflectance normally reported for Spectralon which is 0 99 in air The irradiance reflectivity is the ratio of the total reflected flux to the total incident flux and cannot have a value greater than one On the other hand the radiance reflectance the ratio of reflected radiance to inci dent irradiance may vary as a function of angle A perfect Lambertian reflector would have radiance reflectivity of 1 at all angles but realistic reflectors may have values greater than 1 at some angles indicating a sp
6. accuracy To determine if the plaque is properly wetted submerge it in clean water and view the plaque from various angles When properly wetted it should appear uniformly white from any angle A shiny or splotchy grey ap pearance indicates inadequate wetting To avoid this it may be necessary to rinse the plaque with a wetting agent be fore use We recommend a dilute solution of Kodak Photo Flo 200 which is available from suppliers of photographic equipment Note that Photo Flo is sup plied in highly concentrated form and must be diluted for safe use The best way to wet the plaque is to prepare a 1 200 dilution of Photo Flo 200 in a spray bottle then spray a light layer onto the plaque Submerge it to test whether it wets properly Continue applying more and testing as necessary Ap ply only the minimum necessary and after submerging the wetted plaque in the calibration fixture flow additional clean water over its surface Wetting may also be improved by letting the plaque soak in clean water for several hours after cleaning and rinsing with the wetting solution but do not leave the plaque in water for more than a day After removing the plaque from the calibration fixture stand it up vertically in a sink or tank rinse it thoroughly with clean water and let it air dry 3 PROCEDURES 3 1 GENERAL PREPARATION 3 1 1 Computer You will need a computer with HydroSoft 2 72 or later installed and a free RS232 serial port
7. definitions above 19 4 4 GAINS Each backscattering channel has five discrete gain settings that adjust its sen sitivity over a five decade range They are measured by adjusting the distance to a reflective target until the sensor s response is near its maximum then the gain is reduced by one step and the response to the same target measured on the lower gain This allows calculating the ratio of the two gains from 6 2 S g So g Ga S g D S5 g D Once all four ratios are known the specific G values are determined by defining Gg as 1 for the setting g in effect when u is measured g 1 or 2 That is if u was measured on gain 1 Ged G R G RoR G4 RRR R R R4R If u was measured on gain 2 l R 1 G RjR 20
8. do this place the dark target on the platform of the HOBI Labs calibration fixture Then begin the standard gain procedure selecting the Near option as de scribed in section 3 6 4 After the 5 4 gain ratios have been measured for all chan nels remove the dark target and continue with the white platform itself as the re flective target Dark target for gain calibration of HydroScat 6P 3 6 4 Direction of Motion When you click the Start button to begin the procedure you will be offered the choice of starting with the target near or far from the instrument face Near in this case means closer than the instrument s peak response which is typically 5 12 to 6 cm from its face Far means more than 6 cm and on the highest gain can mean as e sure target is stationary then much as 30 cm You should lick OK normally select Near This will Start keep the target in the Hydro uo ox HydroScat 2 Calibration x Load Store Mu Dark Offsets Gains Scat s most sensitive region re Channel Signal 2 1 3 2 4 3 5 4 quiring less motion of the target qum 10 18 676 The proximity of the target also helps shield the instrument from room lights Note that some instruments have such high sensitivity that some of their channels will satu Help Advanced rate even when the target 15 usen poros moved to its maximum distance in which case you must use the Near option
9. ALLATION The crank handle used to adjust the height of the target platform is detached from the fixture during shipment See the installation instructions on the next page Fixture with HydroScat 6P ready for calibration plaque not shown Crank handle installation thread the handle onto the protruding rod until about 6mm of thread protrudes above the top Then lock it in place with the supplied nut 2 3 CALIBRATION PLAQUE HOBI Labs recommended calibration plaque is a 10 inch square of Spec tralon available from Labsphere Inc North Sutton NH www labsphere com as part number SRT 99 100 2 4 PLAQUE MAINTENANCE Spectralon plaques must be carefully handled and cleaned to maintain their calibrated reflectivity Do not touch the calibrated surface with bare hands Also see the maintenance instructions from Labsphere that come with the material If you purchased your plaque directly from LabSphere note that Lab Sphere plaques are held in their frames with steel screws that rust in water and may eventually stain the Spectralon We recommend you either remove the Spec tralon from the frame for use or replace the screws with plastic or stainless steel versions Plaques supplied through HOBI Labs have stainless steel screws that will not rust When it is completely clean Spectralon very effectively repels water This means air may cling to it when it is immersed which can seriously compromise the calibration
10. Backscattering Sensor Calibration Manual Revision P January 2013 HOBILAbs Hydro Optics Biology amp Instrumentation 5 Laboratories WM Lighting the Way in Aquatic Science www hobilabs com support hobilabs com Revisions Rev P Jan 2013 Change photos to show new fixture design Rev O Aug 22 2010 Formatting revise sections 3 4 1 3 5 3 and 3 6 to include instruc tions for instruments with non flat faces such as Series 250 HydroScat 6 correct Phot flo dilution ratio in 2 4 from 1 100 to 1 200 Rev N Oct 30 2008 Revise recommended plaque wetting procedure 2 4 add Final Steps section 3 8 Rev M 1 2008 Minor edits and formatting improvements Change target to plaque in most cases Rev L July 3 2006 Add note about lubrication Rev K June 15 2006 Add note about Photo Flo wetting agent and other notes about tar get maintenance 2 4 Rev J July 24 2003 Add reference to washers in fixture assembly Rev I May 30 2003 Add Target section 2 2 expand target maintenance section 2 4 add Coefficient Calculations section 4 include a Beta and c Beta in title and over view some minor editorial changes Rev H December 9 2002 HydroSoft 2 6 Changes advanced settings section 3 9 and new recommendation for Rho in yw calibration section 3 5 4 Rev G June 27 2002 Complete revision to incorporate HydroSoft 2 5 calibration func tions Earlier revisions not tracked ii
11. Graph Window Help offset measurements and Q2 ari SSS discards all the results 0 008 V 0 00083 When the measurement 0 007 gue procedure is complete Hydro las Go signa Gona Gorrect Soft will ask whether you wish 0004 to save the raw data in a file The calibration results will not 0 002 0 001 Normalized signal be affected by whether or not e you save the raw data The saved be file cannot be used to directly re 988 produce the results of meas 000 o2 oe os 10 12 14 16 18 20 22 Elapsed Time minutes urements it is only useful for trouble shooting 3 5 MU MEASUREMENT 3 5 1 Preparation Clean the windows attach the mounting collar and place the HydroScat in the calibration tank filled with clean water To calibrate a HydroScat 4 with an in tegrated anti fouling shutter remove the shutter blade The face of the instrument should be fully submerged and it should be level in the tank the face of the in strument should be parallel to the plaque Make sure there are no bubbles on the HydroScat windows and continue to monitor the windows during the procedure to be sure that no bubbles accumulate Also make sure that the plaque is well satu rated with water and there are no bubbles on the plaque If bubbles begin to ac cumulate in either place before the calibration is complete they must be
12. at does not have a flat face for example a HydroScat 6P in its deployment cage use the supplied cover that presses directly against the windows TER TE E Load Store Mu Dark Offsets Gains On the Dark Offsets tab of ollecting offset data the Calibration window click er Start HydroSoft will proceed to EBENE measure the offsets on each of 1655 16 05 15 1639 1656 16 0 4 14 1640 instruments channels and bb470 1655 16 0 3 13 1642 ains displaying the results in a 1659 16 09 12 1644 8 P ying 1714 10 30 1660 table It will also display the raw 1535 16 03 10 1524 data in the graph window Hy bb676 1535 16 0 4 9 1526 droSoft calculates the standard 1553 16 10 19 1524 T lea 5 1623 10 70 1532 deviation of the data while it samples the offsets and continues use 1616 16 04 4 1609 xj averaging on each gain until the maximum uncertainty falls be low the value entered in the Ad vanced Settings dialog box section 3 9 While sampling it highlights the val ues that exceed the uncertainty goal as shown in the illustration Occasionally an outlying point or some disturbance to the setup may prevent the uncertainty goal from being met In this case or for any other reason you can click the Undo button to back up to a previous step in the procedure The Quit button halts the 3 untitled H2000321 HydroSoft ioj xj File HydroScat2
13. ation before saving the gain values 3 6 1 Setup It is usually most convenient to perform this procedure in the same fixture as the calibration However the target can be any object that can be set to stable positions and the measurements need not be done in water If you use water be ware of bubbles or particles that might move during the measurements This procedure should be performed in subdued lighting preferably with no fluorescent lights to avoid excessive noise when measuring the higher gains 11 3 6 2 Basic Procedure To measure the gain ratios you move the target to a position that causes a near peak response from one or more channels on a particular gain setting Then while the target remains stationary HydroSoft measures the response to the target on the current gain reduces the gain one step then measures the response again This is repeated until all gain ratios have been measured for each channel of the instrument 3 6 3 Setup and Procedure for HydroScat 6P As explained in section 3 6 4 it is usually desirable and sometimes essential to measure the instrument response with the reflective target almost touching its face However some instrument configurations prevent this For example those with a built in anti fouling shutter or an integrated deployment cage such as that on the HydroScat 6P In these cases it is necessary to use a low reflectivity dark target for close range measurements To
14. center of the source beam to the center of the scattering site r is the distance along the return path to the receiver Using these relationships HydroSoft can then calculate Zmax Wiz o K 2 Zmin However to enable a much more efficient calculation of o K during processing of in situ data as well as to minimize the amount of information that must be con tained in an instrument s calibration file we desire to simplify the above expres sion Because of the exponential relationship between W K z andW K z o K can be closely approximated by o K ko exp K yk where _ Ino K 3 2 Ky 3 and ky For these coefficients HydroSoft calculates Kp by assuming the calibration water has absorption equal to that of pure water and scattering equal to twice that of pure water While these are obviously crude assumptions their effect on the out come of the computation is very small unless very poor quality water is used dur ing the calibration The value of 3 used in the above expression for kexp was determined empiri cally to provide very accurate fitting of o K for Kj values from 0 to 10 4 3 DARK OFFSETS S g is the residual signal measured on gain g where g designates of five possible gain settings when there is no actual backscattering signal present It is calculated for every gain on every channel by S g S 5 see the vari able
15. data HydroSoft collects as many samples as are required to bring the sample uncertainty below Maximum Uncertainty Raising this value decreases the amount of time it takes HydroSoft to measure the gain ra tios but increases the possible error 3 9 3 Offset When measuring dark offsets HydroSoft decides how many samples are re quired by calculating the statistical uncertainty of the samples it has collected and continues until the uncertainty is below the value specified here Some individual instruments have higher noise levels than others and therefore require more sam ples to achieve this uncertainty In extreme cases the uncertainty may never fall below the threshold in which case the threshold can be raised here 16 4 COEFFICIENT CALCULATIONS The following is a brief presentation of the key equations used to calculate calibration coefficients during the above procedures For a complete description of the theory and mathematics behind the calibration see Instruments and Meth ods for Measuring the Backward Scattering Coefficient of Ocean Waters by Robert A Maffione and David R Dana Applied Optics Vol 36 No 24 20 August 1997 For a description of the electronics and optics of Labs backscattering sensors and how these calibration coefficients are applied to their data see their individual user manuals available from www hobilabs com 4 1 Mu PL SS 8 2 8 42 E cos tan 22 where NS
16. ecular reflection component In this case conservation of energy demands that that the reflectivity be less than 1 at other angles HOBI Labs measurements of Spectralon reflectivity in water show that with incident irradiance at 20 degrees from normal as for the HydroScats its radiance reflectivity at 20 degrees reflected angle is 1 10 4 2 SIGMA Before scattered light is measured by the backscattering sensor it must travel from the sensor to the scattering site and back Over that distance some light will be lost to the water s attenuation resulting in an underestimate of scattering For clear waters this is insignificant but as turbidity increases so does the underesti mate of scattering To compensate for this calibrated backscattering values are multiplied by the function o has a value of unity for very clear wa ter and increases as attenuation characterized by the coefficient increases The response function collected in order to calculate u that is S z is also used to derive Kp which is define as follows IL m o K wes z dz 0 where Kbbw is Kps of the water in which the sensor was calibrated and 22 cos tan H 2z It can also be shown that having measured W 2 during the calibration pro cedure one can then calculate for any Ky W K z W Ky z exp Ky Ky Yr where 18 r is the distance along a line from the
17. ed Calibration 14 NOTE HydroSoft does not automatically adopt the new calibration into its existing data windows That is if you collect new data from your instrument after completing the calibration HydroSoft will still display it with the old calibration values unless you explicitly load the new calibration from a file or from the in strument by reconnecting to it 3 9 ADVANCED SETTINGS If you click the Advanced button new in version 2 6 in the calibration dialog box the following dialog will appear and allow you to control parameters of the calibration process In most cases you should leave these set to their de faults 3 9 1 Mu During the calculation of u only data collected at ranges greater than or equal to the First Valid Range will be included in the calculation This is independent of the Starting Distance you set on the tab of the main calibration dialog The Starting Distance informs HydroSoft of the actual distance at the beginning of 7 calibration whereas the First Valid Range prst vaid Range Es am controls what range of data will actually be Total Range fs em included in the calculation This setting is Maximum Slope 001 per cm required because signals at shorter ranges P r Gain are dominated by multiple reflections be Saturation Threshold 30000 counts tween the instrument face and the calibra ee Optimum High Signal 25000 cou
18. gains When the gain measurement procedure is complete HydroSoft will ask whether you wish to save the raw data in a file As with the offset measurements this is offered strictly as a backup in case troubleshooting is required The calibra tion results will not be affected by whether or not you save the raw data 13 3 7 STORING CALIBRATION RESULTS When you complete each calibration procedure the corresponding check box under New Calibration Data on the Load Store tab will become checked and en abled This indicates that the newly measured values have been copied into the revised calibration You can uncheck them if you decide not to use the new data or if you wish to compare the new and old values in the Revised Calibration win dow opened by clicking on the View Edit button If you leave this window open while checking or unchecking the new calibration options you will see the values change immediately to reflect your selections You can also compare the values side by side by opening both the Baseline Calibration and Revised Cali bration windows In the Revised Calibration window you can click on the lock icon to enable direct editing of most of the calibration values Once you are satisfied with your calibration results you can save them in the instrument s memory in a file or both When you click the To Instrument button HydroSoft will transmit the complete calibration to the instrument check to verify that it was co
19. harging circuitry in the Hy droScat 6 can also cause noise in the measurements Allow the instrument to stabilize for several minutes before beginning the calibration procedure 3 2 STARTUP In HydroSoft connect to the instrument and verify that it is communicating properly Except in special cir cumstances you should check the wu Dark offsets Gains Load Calibration From Instru Baseine calibration ment option in the connection dia Source Pydrascat Hanna log box This will ensure that the From Instrument From File View revised calibration you generate contains the correct configuration information about the instrument New Calibration Data Sama 275 Gain Select Calibrate from the Revised Calibration HydroScat menu which will dis Saved ta Not saved play the following dialog box To Instrument To File View Edit This contains four tabs that control the different calibration processes Help Advanced Close 3 3 BASELINE CALIBRATION HydroSoft builds new calibration files by combining newly measured data with baseline data from the instrument or from a file Data that are not revised during the calibration procedures are copied directly from the baseline to the re vised calibration Baseline data include channel names wavelengths and other as pects of the instrument configuration so it is very important that the baseline match the
20. iarity with it and discusses the details of HydroSoft that pertain strictly to calibration For further introduction to HydroSoft and its other features consult the HydroSoft User s Manual and also the manual for the instrument to be calibrated 1 6 CALIBRATION RESULTS Finished calibration data are stored in structured text files on a computer and also stored in each HydroScat s internal memory Normally the calibration stored in the instrument is considered authoritative and is downloaded from the instru ment whenever HydroSoft communicates with it However HydroSoft can also be instructed to ignore the instrument s internal calibration and use a file instead 2 CALIBRATION FIXTURE 2 1 DESCRIPTION HOBI Labs standard fixture for the and gain ratio calibrations consists of an acrylic tank containing a platform that can be raised and lowered in precise increments diffuse white plaque is placed on the platform and the tank filled with water The instrument is placed with its face under the surface of the water facing the plaque The plate is then moved throughout the instrument s sensitive range according to the procedures be low HOBI Labs has built cali bration fixtures of several sizes and styles The descriptions in this document reflect the design first manufactured in 2013 This is functionally identical to the previous design shipped from 2001 to 2012 but is smaller and lighter 2 2 HANDLE INST
21. instrument being calibrated Usually the instrument s internal calibra tion is used as the baseline When you first open the Calibrate dialog box the calibration that is in effect in the data window from which it was opened is adopted as the baseline There fore it is not usually necessary to explicitly select a baseline However you can load the baseline from a file using the From File button or from the instru ment s internal calibration with the From Instrument button Whenever you se lect a new baseline baseline data are immediately copied to the revised calibra tion but they will not overwrite any new calibration data you have collected Clicking the View button will open a window in which you can browse the contents of the baseline calibration You can leave this window open while pro ceeding with the calibration in order to compare the baseline and revised data 3 4 DARK OFFSET MEASUREMENT This procedure does not require use of the calibration fixture It is not re quired for the calibration but it is advisable to update it every time the u calibra tion is performed It is required whenever the gain calibration is performed 3 4 1 Set the HydroScat face down on several layers of black felt or similar mate rial Be sure the HydroScat is on a flat surface and that its face is in contact with the covering material so that no light can possibly travel between the windows If the HydroSc
22. ion this document only applies to calibration of their backscat tering measurements measured by recording the signal value while a channel is set to a certain gain changing the gain by one step and recording the new signal value 1 4 SEQUENCE OF PROCEDURES For a complete calibration the most convenient sequence is usually to meas ure the dark offsets first since this is done outside the calibration fixture then per form the u calibration then the gains However it is not necessary always to per form all three steps and their sequence is also not fixed Because the gain ratios are the most time consuming to measure and also the most stable of the instru ment s characteristics you may not wish to measure them as often The calibration and dark offset measurements are independent of each other and can be performed by themselves at any time The gain ratio calibration requires that the dark offsets also be measured It is most intuitive to measure them before performing the gain ratio procedure but it is also acceptable to reverse the sequence HydroSoft will remind you if offsets are required to complete a gain 1 5 HYDROSOFT SOFTWARE HydroSoft version 2 5 and later 2 72 or later recommended guides users through the necessary calibration procedures collects and processes the data and stores finished calibration results HydroSoft is also used for routine operation of the sensors so this document presumes your famil
23. nts tion target and the actual backscattering minimum High signal 555 signals are negligible Minimum High Signal gain 2 sooo counts Minimum Total Range and Maxi Maximum uncertainty 002 per count mum Tail Slope determine the total range of data that HydroSoft will require for a Maximum uncertainty s calculation HydroSoft will only calculate if the range of data included is at least Restore Defauts equal to Minimum Total Range It also requires that the slope of the curve s tail is below the Maximum Tail Slope A low tail slope indicates that no further information would be gained by measuring at larger ranges For example the default value of 0 001 means that each addi tional cm of range would change the u value less than 0 1 3 9 2 Gain The first four gain parameters control how HydroSoft determines the signal levels it will require for measuring gain ratios As described in section 3 6 the program will direct the user to adjust the target distance until at least one of the 15 channels is above Optimum High Signal but below Saturation Threshold Then it will measure the gain for that channel and any others that are between Minimum High Signal and Saturation Threshold A different Minimum High Signal is set for gain 2 because some instruments do not have enough overall gain to reach the regular threshold on that gain When collecting gain ratio
24. opriate to the Hydro Distance 24 38 Scat measurement geometry First Step Eja From File HydroSoft remembers values you channel Gain Baseline Integral Rho sig Sig k1 enter so previous values may still 2 0004 6830 L1 5 126 0 42 D 998 1 0 0009 1 623 1 1 21 57 0 149 0 934 appear even after you upgrade the program Once you enter a new value it becomes the default Mu calibration complete Stem Because the previous Rho value was low previous Help prea Ta calibrations based on that value and the backscattering values based on them are also low To compare data based on old and new rho values you should multiply the old data by 1 12 that is 1 10 0 98 10 7 208 5 HydroSoft File HydroScat 2 Graph Window Help No Data 36819360 6 gt 9 44 1 5 si Channels bb470 Iv bh676 Iv 1676 No Sigma C Sigma Correct Normalized signal Distance crn 3 5 5 Loading a File You can load u curves from a previously saved file and recalculate their values by clicking the From File button and selecting a suitable file 3 6 GAIN RATIO MEASUREMENT This procedure is the most involved of the three but because the gain values are normally extremely stable it is also not required very often Note that the gain ratio calculations require that you also perform the dark offset calibr
25. or USB serial adapter in order to collect the calibration data For information on setting up and using HydroSoft see the HydroSoft User s Manual For the u and gain calibrations you should locate the computer near the calibration fixture in a position that allows you to view the screen and type on the keyboard while turning the crank handle on the fixture 3 1 2 Environment Avoid bright AC lighting and especially fluorescent lights during the gain calibration On high gain settings AC lights can cause substantial excess noise 3 1 3 Calibration Fixture and Plaque For the u procedure be sure the calibration fixture is clean and filled with clean water The water need not be perfectly pure but distilled deionized or oth erwise purified water will give the most accurate results Check the plaque for cleanliness and for bubbles or any film of air clinging to its surface A gray or shiny appearance indicates that the plaque is not completely wetted see also sec tion 2 4 It is preferable to fill the tank by placing the outlet of a hose near the bottom of the tank under the water to avoid generating bubbles 3 1 4 Instrument Setup Be sure that the instrument either has external power supplied or its internal batteries have enough charge to operate it during the calibration It is best not to power the instrument from its battery charger during the calibration as this raises the instrument s internal temperature Using the fast c
26. rrectly received and if so ask whether you wish to save it in the in strument s nonvolatile memory If you choose not to the calibration you just loaded will remain in effect until the next time the instrument is reset A reset can be caused by a loss of power including use of the battery disconnect function of battery powered HydroScats by an explicit reset command sent to the instrument or by the Reset command on HydroSoft s Instrument or HydroScat menu If your baseline calibration was loaded from the instrument and you subse quently save a revised calibration to the instrument the baseline retains its former values until you explicitly reload the calibration from the instrument If you re load the calibration you will no lansse beable dev heod g p Load Store Mu Dark Offsets Gains baseline with the new values r Baseline Calibration Source HydroScat 2 H2000321 3 8 FINAL STEPS From Instrument From File View When you are completely fin ished with the calibration you should close the Calibration dialog box before disconnecting the in strument or putting it to sleep During the calibration process Hy droSoft changes some settings of the instrument and it sends com mands to restore these settings at Help Advanced the time the dialog box is closed New Calibration Data Mu Sigma Offsets Gains Revis
27. seconds When this process is complete turn the crank handle one turn if your calibration fixture has 1 27 mm thread pitch fixtures manufactured before June 2002 or gt turn if it has 2 54 mm pitch fixtures made since June 2002 then click Next Step or press the enter key Continue clicking Next Step after each turn or half turn HydroSoft will display the evolving curves in the data window and automatically determine when adequate data have been collected see section 3 9 1 for details At that time it will beep and display a message informing you that you can either continue collecting further data or click the Finish button to calculate the final results and transfer them to the revised calibration 3 5 4 Plaque Reflectivity You can directly enter reflectivity values in the Rho column of the u results table either before or after collecting the data curves The u values will be recal culated each time you change Rho For Spectralon plaques you normally use the default value of 1 10 for all channels Note that the Rho value of 1 10 was introduced December 2002 de fault value of reflectivity in previous HydroSoft versions was 0 98 based on ir radiance reflectivity measure ments provided by Labsphere toad Store Dark offsets Gains HOBI Labs revised this based on stat careful measurements of the radi Start Distance o ance reflectivity in water and at Distance step 127 angles appr
28. ugh the calibration to make it as straightforward as possi ble The calibration has three primary parts coefficients dark offsets and gain ratios described below 1 1 MU COEFFICIENTS Mu 4 is the overall coefficient of sensitivity for a channel which allows converting its normalized electronic response to absolute backscattering This is measured by continuously moving a target plaque with known reflectivity through a range of distances in front of the sensor The resulting curve is integrated and weighted by known geometric factors in order to calculate u 1 2 DARK OFFSETS Because of electronic factors the instrument may produce a non zero signal even when no scattering signal is present These offsets which vary from channel to channel and with gain setting are measured by blocking the face of the instru ment to prevent any light from the LEDs from entering the receivers The dark offsets are measured out of water The HydroScat uses the dark offset measurements internally subtracting them in real time from the raw data it produces 1 3 GAIN RATIOS HydroScats have five different gain settings These are different levels of signal amplification which allow automatic operation in a wide variety of condi tions The lower gain settings also make possible the method of using a highly re flective plaque for the calibration The ratios between adjacent gain settings are a Beta and c Beta also measure attenuat
29. wiped away and the calibration must be restarted 3 5 2 Setting the Channel Gains The first step in calibration is to determine which gain best matches each channel s sensitivity to the calibration plaque This requires monitoring the sig nals while moving the plaque through the sensor s peak response zone To do this click the Start button then follow the on screen instructions 3 5 3 Measuring the Response Curves After the gains have been properly set HydroSoft will instruct you to move the calibration plaque target to its starting position For instruments with flat faces move the platform until the plaque is as close as possible to the face of the instrument without actually touching it and leave the Start Distance set to its default value of 0 cm For a Series 250 HydroScat 6 with its deployment frame installed set the Start Distance to 1 3 cm and move the plaque until it almost touches the frame ring For other instruments with non flat faces for example a HydroScat 4 with an integrated anti fouling shutter measure the length of the longest protrusion for the face and enter that value as the Start Distance For all instruments confirm that the Distance Step entered in the form is ap propriate normally 1 27 mm When the target is set to its starting position click the First Step button HydroSoft will open a new graph in the data window and perform some other ini tializations that may take a few
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