Frequently Asked Questions

Q1 - How is transmitter power specified?

We follow the normal practice of specifying the sound pressure level (SPL) at a distance of 1 metre (i.e. dB re 1 µPascal @ 1 metre). For comparison purposes:

Q2 - What is the radiation pattern?

The radiation of transmitters is omnidirectional (i.e. a spherical pattern). Monitoring receivers (e.g. VR2W and VR3) have a similar pattern.

Q3 - How much variability is there in power level and directionality?

Some variability in power level from unit to unit and deviations from perfect omnidirectionality is inevitable. Even expensive calibrated hydrophones (just the inverse process with the same type of transducer) typically exhibit:

• Unit to unit variability of ±3dB
• Deviation from omnidirectionality in an individual unit of ±2dB

VEMCO has conducted an extensive measurement program and comparable figures for V9 transmitters are approximately ±4 dB unit to unit and ±2 dB from perfect omnidirectionality.

Q4 - How is the output level of transmitters measured?

The normal way to measure output level is in a tank with a calibrated hydrophone but the process is not straightforward due to echoes. Figure 1, taken from a small tank measurement, shows the difficulty. As the figure shows, one needs to capture the raw signal and determine the amplitude once steady state is achieved and before the first echo arrives.

In the case above, the shortest echo path is about 1 metre longer than the direct path and, given that sound travels approximately 1.5 metres in 1 millisecond, the time slot in which the measurement can be made is well under 1 millisecond long. In a larger tank, the time slot would be longer but for these 10 millisecond pulses, the path length of the first echo would have be at least 15 metres longer than the direct path for the whole transmitted pulse to be seen without distortion from echoes.

Q5 - Can one make relative measurements in a tank using a Spectrum Analyzer?

No. While one might assume that, regardless of distortion, one could compare the relative levels of two transmitters by measuring the total spectral energy, the problem is that even minor differences in positioning can have a significant impact of how echoes and direct signal combine. As a consequence, even the same transmitter positioned as carefully as possible each time can produce markedly different results in successive measurements (see Figure 2). Therefore, measurement of energy in a tank where echo strength is significant is meaningless.

Key points to note in Figure 2 include:

• Although the shapes (and energy content) of the two waveforms are vastly different, the signal amplitudes before the first echo are the same.
• The differences as echoes start to arrive are explained by the short wavelength at this frequency (approximately 1.5 cm) so that a positioning variation of even a fraction of a centimeter can change interference caused by a given reflection from constructive to destructive and vice versa.

Q6 - How does S64k coding affect detection performance?

An S256 coded transmitters transmits a 16 bit payload containing an 8 bit ID and 8 bits of sensor data. In the case of a two sensor versions, a separate transmission, each with a different ID, is sent for each sensor.

For the new S64k coding S256 transmissions are made as above alternately with R64k transmissions. This is illustrated below:

• Single Pressure Sensor
  R64k      S256_P      R64k      S256_P      R64k .....



• Pressure and Temperature Sensor
  R64k      S256_P      R64k      S256_T      R64k      S256_P      R64k .....

Impact on Collisions
A question many users ask is what effect the above scheme will have on collisions. To answer this, note that as long as one uses the same delay, the old S256 and the new S64k schemes have the same duty cycle and therefore there is no difference in the collision rate between the two schemes.

Sensor Data Update Rate
The penalty one pays for increasing the ID space is that with the S64k scheme, only half the transmissions contain sensor data. This presents the user with a trade off between:

1. Accepting that such a decrease in data rate is not an issue, or



2. Halving the delay to restore the data rate to what would be achieved with S256 coding.

The second choice is not practical if high residency situations are anticipated. The table below presents results from our analysis of detection performance - defined by the average time between successive detections of a particular tag - as a function of delay and residency. These results lead to the conclusion that for high residency situations, sensor data update rate will be determined by delay and number of resident tags rather than the actual rate that data is transmitted and further, that setting delay too short can have disastrous results.

Note that the update times for one tag present are double the delay which reflects the fact that detections will alternate between the R64k and S256 codes.

Q7 - What is the smallest VEMCO Transmitter?

All VEMCO tags to date have been encapsulated in a rugged cylindrical package. In 1997, we introduced the V9 (9 mm diameter) family of miniature transmitters and in 2004 introduced the V7 (7 mm diameter) family. The V7-1L, the smallest member of the V7 family is 17.5 mm long and weighs 0.7 g in water. In the spring of 2008, we introduced the V6, which is 6 mm in diameter and weighs 0.5 g in water.

Q8 - What is the difference between continuous and coded transmitters?

Continuous transmitters ping continuously from the first ping until power is lost. These transmitters are identified by the operating frequency and the period if they do not transmit data. Coded transmitters use a series of pings to form unique "ID codes" followed by a period of silence. The period of silence can be multiple minutes long, thus providing time for other transmitters to be detected with minimum overlap or "code collision".

Q9 - Should I use coded or continuous transmitters?

Continuous transmitters are useful for experiments where the scientist needs to track individual animals from a boat.

Coded transmitters are designed for automated monitoring experiments where low cost single channel receivers can be distributed throughout a study area to detect the time and date of passage of each tagged animal. It is possible to track coded tags from a boat but the more sophisticated VR28 receiver is used because it indicates the direction to the transmitter with each code received. Tracking of infrequent codes with a VR100 receiver and directional hydrophone is difficult and tedious because of the infrequent repeat rate of the code. However, it is possible to do simple grid searches using a VR100 receiver.

Q10 - What issues are involved with possibly thousands of ID codes on a single frequency?

It is important for the researcher to realize that one receiver can only detect one ID code at a time. If two codes overlap at one receiver site then neither code will be detected. Because of randomization of Delay Time (the silence between transmissions), the next time these two tags transmit, the chances are that they will not collide and both will be detected. The choice of the average Delay is important because it will influence how many tags can be detected in the same location. The average time between detections depends on the number of transmitters present and transmitter Delay Time. VEMCO provides an on-line Collision Calculator which calculates collision statistics including average time between detections. Some representative results for A69-1303 (R64k SYNC = 320) coding are shown in the table below.

For site residency studies where fish may be present for many days, the average delay can be multiple minutes or longer. However, for fast moving fish migrating through river systems, consideration should be given to their expected transit time past a fixed receiver site.

Note that the above values are calculated with a simulator using randomly selected ID codes. There will be some variation depending on the ID codes used together.

Q11 - Why does Vemco use 69 kHz for its miniature tags when other vendors seem to use higher frequencies?

VEMCO has the capability to produce miniature tags operating at any frequency from 40 kHz to over 400 kHz.

However, with few exceptions - most notably 180 kHz in noisy environments around hydroelectric dams - we have concentrated on 69 KHz which has served our clients well since this low frequency gives good range in both salt and freshwater environments. For instance, using V9s, researchers have been able to reliably detect passage (close to 100% detection rate) with VR2W monitoring receivers spaced 500 to 800 metres apart.

The use of a single frequency also has the huge advantage of making possible a "worldwide network" in which every tag can be detected by any receiver in the world.

The use of a low operating frequency does, however, involve compromises and as we continue to reduce the size of our transmitters, a point of diminishing returns is reached due to the very low efficiency one can achieve when driving a small transducer far below its resonant frequency. Therefore, starting with the V6 family (6 mm), a low frequency version becomes impractical and for this reason the family will use a standard transmission frequency of 180 kHz. To maintain the worldwide network concept, future high end receivers (V4, VR100, etc.) will detect both 69 kHz and 180 kHz tags. The low cost VR2W receivers will continue to be single frequency and therefore, one will need a second receiver if one wishes to detect both 69 kHz and 180 kHz.

Q12 - Can you comment on how to determine the minimum recommended fish size for a particular sized transmitter?

In general, we tend to rely on the expertise of expert biologists to answer questions like this and do provide a list of useful references.

Past studies have reported that tag implantation affects survival, growth rate and swimming performance of fish (Lacroix et al. 2004; Perry et al. 2001; Moore et al. 1990; Adams et al. 1998a, 1998b; Chisholm and Hubert, 1985). The general rule that biologists follow is that tag air weight should not exceed 2% of fish weight. However, many biologists have exceeded these guidelines. For example, Lacroix et al. 2004 determined that juvenile Atlantic Salmon can carry a tag that weighs up to 8.5% of body weight with minimal effects compared to a control group of untagged fish. They showed that growth and swimming performance is slightly delayed for a short period after surgery. However, tagged fish soon catch up with the control group. Fish health, weight, shape and swimming style are important factors to consider and researchers should perform controlled studies relevant to their fish species.

Q13 - What type of sensor transmitters does VEMCO sell?

• Temperature
• Pressure
• Temperature and Pressure
• Accelerometer and Pressure

Q14 - Would VEMCO consider developing other sensor transmitters?

Yes. We are continually looking for good opportunities so please send us your ideas.

Q15 - What is the accuracy and resolution of your temperature transmitters?

The accuracy of the temperature in our temperature transmitter models is primarily determined by the manufacturer of the sensor and is specified as follows:

• -5°C to 35°C temperature range tags, approximately 0.5°C accuracy
  and 0.15°C resolution



• -4°C to 20°C temperature range tags, approximately 0.5°C accuracy
  and 0.1°C resolution



• 0°C to 40°C temperature range tags, approximately 0.5°C accuracy
  and 0.15°C resolution



• 10°C to 40°C temperature range tags, approximately 0.5°C accuracy
  and 0.12°C resolution

Q16 - What is the accuracy and resolution of your pressure transmitters?

The accuracy of the pressure in our pressure transmitter models is primarily determined by the manufacturer of the sensor and is typically specified as being ±5% of the full scale value (the maximum depth) at room temperature. This translates as follows:

Q17 - Why doesn't VEMCO specify pressure accuracy for sensor tags across temperature ranges?

Background
VEMCO developed the pressure sensor line of transmitters in response to customer demand for a low cost means of determining relative depths of tagged animals. Two important constraints are thusly placed on the sensors:

1. Physical size: the sensor and associated hardware and processing elements must fit within the general physical dimensions of the existing transmitters (9mm, 13mm and 16mm diameters)



2. Cost: the cost of the sensor and associated processing hardware and algorithms must not drive the cost of the transmitter excessively high.

Discussion
For the purposes of application in VEMCO transmitters, pressure sensor errors are dominated by non-linearity in readings across the pressure range and changes in the pressure sensing characteristic at various temperatures. Although pressure sensors are available on the market that have excellent linearity and temperature compensation, they are expensive (>$1,000) and typically much too large to fit in even a V16 package.

The pressure sensors that are available in the price and size range suitable for use in VEMCO transmitters are typically specified by the manufacturer to be within 10% of the full scale value (e.g. within 5 meters for a 50 meter rated pressure sensor) at room temperature only. The manufacturers do not specify accuracy at temperatures other than room temperature.

From in-house testing of the sensors at various temperatures, we know that the sensors will either have more error at greater depths than at shallow depths when they are cold or they will have greater errors at shallow depth and less at greater depths when they are cold.

Calibration
VEMCO performs calibration on each pressure transmitter in a calibrated pressure test tank by taking readings at several known pressures. The algorithm adjusts and normalises the slope and intercept values such that reading errors are minimised across the pressure range. This calibration is performed at room temperature. In order to properly calibrate-out temperature errors, pressure calibration would need to be performed across the full pressure range at several temperatures and fed into a complex algorithm. To do this will add considerable cost to each transmitter and the calibration's validity would be questionable over time. It is also improbable that the complex calibration equations would easily fit into the limited computing resources of the transmitter.

It is possible to do a cost effective calibration/adjustment at lower temperatures at 0 PSI (as is the case with some competitors). This would have the effect of making the pressure sensor appear more accurate when tested by our customers in their labs. However, the nature of the pressure sensor characteristic as discussed above is such that this type of calibration will probably increase errors in readings in low temperatures at depth.

Q18 - What types of receiving equipment does VEMCO offer?

Receiving equipment falls into two broad classes:

Tracking Receivers such as the VR100 (and the VR60 which it replaces) and the VR28 which are intended for use on a boat where one follows tagged fish or goes to an area to find out which fish are there.

Monitoring Receivers which are typically installed as fixed arrays to support migration studies (large scale movements) or residency studies (detailed movements in an area).

We use two general architectures for receiving arrays:

• Widely spaced arrays of VR2Ws or VR3s. These receivers are autonomous and perform all receiving and data processing functions. No cabling is used. The VR2W needs to be recovered to obtain data while the VR3s communicate data back to the user by a variety of methods - currently Argos satellite or underwater modem but the architecture supports easy development of other versions such as radio, wireless or wired network, other satellites, etc.



• The VRAP System uses up to four receiving nodes each precisely measuring the time of transmitter signal arrival to provide precise location of tagged fish (1 metre precision or better) within the array. Typical spacing between receiving nodes could be 500 to 100 metres depending on the transmitter used. There is no cabling between nodes and communication to a shore base station providing real-time display and logging of tagged fish position is by radio.

Q19 - Can I use the signal strength indication of a VR28 to estimate range to the transmitter?

First, it is important to realize that estimations of range based on signal strength cannot be precise. There are many factors which can cause the signal strength at a given range to differ from a theoretical value calculated from transmitter power and transmission losses due to spreading and absorption. It is also quite common to see significant fluctuations in signal strength even if range doesn't change. So in using the suggested procedure below, you should, first, regard it as giving a very approximate estimate of range and second, you shouldn't attach too much significance to short term variations in signal strength.

The basis to estimating range is to note that the VR28 uses automatic gain control which increases the gain as the signal strength gets less - i.e. the larger the gain displayed the weaker the signal and therefore, the greater the range. You could do a rough calibration of this by conducting a range test with a typical transmitter and noting the value of the gain display for each range. Note that this "calibration" would change if you used a transmitter having different output power from the one you used for the range testing.

Q20 - What is receiver initialization?

Initialization is an important step required to configure your receiver correctly. During initialization, you can input the station name (location) where the receiver will be deployed (VR2W only) and set the receiver clock based on your computer clock. The receiver clock is always updated based on your PC clock during initialization. This information will be resident with the receiver and will be available during upload regardless of whether you use the same computer or not. Initialization also erases the receiver log files so be sure to upload data from your receiver before initializing it. When data is uploaded from a receiver, the VRL file contains information about how the receiver was initialized.

If a VR2W receiver is deployed without being initialized, the receiver will detect tags but the receiver will not necessarily have the correct clock setting or map configuration that are required for proper data detection.

VR2 receivers must be initialized before deployment or they will not detect tags.

Q21 - How/when do I change my receiver code map?

Receivers must be configured with a Code Map that defines which type of tags the receiver can detect. Check www.vemco.com/maps.php for details on currently supported Code Maps and choosing the proper map for your study. Changing a receiver map is not done often and should be done with careful attention. Setting up a receiver with an incorrect map may result in no detection data which would not be discovered until the user retrieves the receiver and uploads the data. When a receiver is configured with a new map, the data logs are automatically erased as they are no longer valid in the presence of a different code map. Please upload stored data prior to installing a new code map.

See the receiver specific sections of the VUE Manual for detailed instructions on configuring your receiver with a new code map.

Q22 - During a range test, I noticed that not all transmissions were detected when I was close to the receiver but as I moved further away, the detection rate improved significantly. What's going on?

The problem is caused by a severe echo situation. VEMCO receivers reject echoes by implementation of a Blanking Interval, the idea being that after detection of a pulse, the receiver ignores all potential pulse detections until this period of time has passed.

As long as echoes arriving after the Blanking Interval are below the receiver's threshold, everything is fine, and due to the conservative approach we take, this is almost always the case. However, in certain situations, it is not. If that happens, the extra pulses result in a failure to properly decode the code sequence and, consequently, there is an apparent loss of signal. So if you were using a tracking receiver such as the VR100, you would hear a stronger signal as expected at short range but the receiver would not always successfully decode it.

Q23 - My VR60 is showing minus numbers for coded R64K tags? Why?

The VR60 receiver is still a useful receiving tool but is based on dated technology (R64K tags were not invented yet!). When the VR60 was designed, tag ID's over 32768 were not envisioned by VEMCO. With increasing usage of our product and emerging technology, new ID schemes have been utilized to bring about more functionality and ease of use.

This has therefore caused a minor issue with the VR60 receiver. The VR60 can decode R64K tags with ID's over 32768 but will display them as a minus number decreasing from 32768 to 0. Therefore, a tag with ID 32769 (and so on) will display as -32767 on the display of the VR60. While the VR60 will not properly display these higher ID codes in post processing, simply adding 65536 to the ID will result in the correct tag value being attained. So, the ID 32769 will display as -32767. Add 65536 to this to give the following:

• -32767 + 65536 = 32769 (the correct tag ID)

Here is another example. This tag

gives you this ID.

The calculation is as follows:

• -1536 + 65536 = 64000 (the correct ID)

VEMCO announced the VR60 was going obsolete in our February 2007 newsletter (www.vemco.com/news/vr60_obsolete.php). The current R64K tag is the last generation of tag that the VR60 will be capable of decoding. Therefore, users of the VR60 should consider upgrading to the VR100 (www.vemco.com/products/receivers/vr100.php), a newer generation of VEMCO receiver that will detect and decode all current and future tags. Feel free to contact VEMCO Sales at for up-to-date pricing and availability.

Q24 - Will VEMCO RS-232 products (VR2PC interface and Minilog reader software) work with a USB-RS232 adapter?

See the USB-RS232 Adapters Troubleshooting document.

Q25 - VUE does not detect the Bluetooth adapter. What do I do?

VUE will display a Bluetooth logo in the bottom right hand corner of the main window when the Bluetooth adapter is detected and functional. If it is not detected, a red X will appear over the logo.

  

Here are some things to check if VUE does not detect a Bluetooth adapter:

1. Is the VEMCO-supplied Bluetooth adapter installed in a functional USB 2.0 High-Speed port on your PC? VUE will not work properly with any adapter other than those supplied by VEMCO.



2. Are you running the latest version of VUE? The model of VEMCO-supplied Bluetooth adapter may change from time to time. Updating to the latest version of VUE is the best way to ensure compatibility. See VUE Software Support for the latest download.



3. Are incompatible drivers installed? Drivers for the Bluetooth adapter must be installed through VUE. Do not install drivers from any other source. The drivers distributed by the original manufacturer of the Bluetooth adapter are not compatible with VUE. If you previously installed the Belkin Bluetooth software, you must remove it before installing the VUE drivers.



4. Is the VEMCO Bluetooth driver installed? Use the VUE Bluetooth installation tool (located under the "Tools" menu) to install or reinstall the correct device driver.
   
   
   
   You will require administrator access to the PC to install the device driver. If no adapter is found, your Bluetooth adapter or USB port is not functional.





5. Is the BTH.INF file missing? This driver information file is a standard part of the Windows system, however some computer manufacturers rename or delete it to force customers to use a particular set of Bluetooth drivers. This file should be located at C:\windows\inf\BTH.INF. If it is not present, it may have been renamed to C:\windows\inf\BTH.BAK. Simply rename this file by replacing .BAK with .INF and rerun the VUE driver installation.

Q26 - My receiver does not appear in the VUE receiver list. How can this be fixed?

VUE will display a green check mark icon next to the name of a receiver in the receiver list when an active Bluetooth signal is detected.

Receivers are automatically added to this list when they are first detected. There are a number of things that may prevent a receiver from being detected.

1. Does VUE indicate that your Bluetooth adapter is functional? (See FAQ 25)



2. Is the VR2W Bluetooth signal enabled? The VR2W status light will flash once a second as long as the Bluetooth signal is enabled. Consult the VR2W manual for details.



3. Have you waited long enough for the receiver to be detected by VUE? VUE will immediately start scanning when the application is launched. You may have to wait up to 30 seconds after the receiver Bluetooth is enabled for the receiver to appear in the VUE receiver list. While you are actively communicating with one or more receivers, additional receivers will take up to 2 minutes to appear in the receiver list.



4. Is the VR2W placed within range of the Bluetooth adapter? Try moving the receiver closer to the Bluetooth adapter and eliminating any possible sources of radio interference.



5. Is there a second Bluetooth adapter installed on your PC? A second Bluetooth adapter, such as a built-in adapter on a notebook PC, can interfere with the VEMCO-supplied Bluetooth adapter in some circumstances.
   
   
   Try removing or disabling the other adapter. If you are unfamiliar with the Windows Device Manager, please consult the Windows documentation for details. You will require administrator access to the PC in order to disable devices.



• Open the Windows Device Manager.
• Open the list of Bluetooth Radios.
• Disable any radio devices other than VEMCO devices using the "Disable" action. Do not disable the "Microsoft Bluetooth Enumerator".
• Remove the VEMCO Bluetooth adapter from the USB port and reinsert it. It should reappear without the yellow exclamation mark.

Q27 - When I attempt to open my receiver in VUE, the error message "Failed to open Bluetooth Device" appears. What should I do?

This occasionally occurs when the VR2W Bluetooth hardware is defective. Please contact Customer Support.

Q28 - When I attempt to open my receiver in VUE, it connects for less than a minute and then disconnects. Why?

This occasionally occurs when a Bluetooth adapter other than the VEMCO-supplied Bluetooth adapter is used. If your PC has a built-in adapter, it may be overriding the VEMCO adapter. You will need to remove or disable the other Bluetooth adapter. Please refer to Point 5 in FAQ 26.

Q29 - Will VEMCO RS-232 products (Minilog reader software and VR2PC interface) work with a USB-RS232 adapter?

See the USB-RS232 Adapters Troubleshooting document.

Q30 - How do I use the values of Syncs, Pings, Detects and Rejects to assess the quality of my study deployment?

Syncs, Pings, Detections and Rejects
The VR2W receiver event logs provide an account of the Daily Syncs, Daily Pings, Daily Detections and Daily Rejects for the duration of your receiver deployment. These are defined as follows:

• Daily Pings - a Ping is a pulse transmission from a VEMCO transmitter - typically at 69kHz. VEMCO tags have 8 or 10 pings per transmission depending upon the type of tag coding used.



• Daily Syncs - a Sync is the interval between the first two pulse transmissions (pings) from a VEMCO acoustic tag. VEMCO receivers are programmed to detect specific Sync intervals measured in msec. This interval is used by the VEMCO receivers to determine the type of tag transmitting.



• Daily Detections - a detection is a record of a valid transmission from a VEMCO transmitter. The record includes the time stamp and the transmitter ID. Daily Detections are accounted for each type of VEMCO tag detected (A69-1105, A69-1303, etc.).



• Daily Rejects - a reject or rejected detection is counted every time the VEMCO receiver detects a sequence of pings that have the correct Sync value, the correct number of pings and the correct interval spacing to be considered a valid VEMCO tag transmission, but fail to pass the VEMCO Error checking algorithm. These usually occur as a result of tag collisions.

Reviewing these statistics can be a valuable aid in determining remedial actions when the performance of an acoustic study does not appear to be as you had expected.

The SYNC values are very specific and unlikely to occur, in any number, randomly in nature. Therefore, the presence of SYNCs is a clear indicator that VEMCO transmitters are within range of the receiver. If the number of Detects is equal to or close to the number of SYNCs, you have a normal operating system and most tag transmissions are being recorded as detections. Some level of tag collisions is expected which will mean the Detects will be less than the SYNCs. The number of Pings should be roughly 8 times the number of detects.

If you have a large number of SYNCs but your number of Detects is much lower, this suggests significant collisions from a large number of tags present. This is normal operation and does not indicate any need for remedial action as long as you are getting the amount of data and thus information as required out of your study. In a high collision situation, you would also see a significant number of Rejects.

If your number of Detects is vastly lower than your number of SYNCs, or you have very few Syncs and Detects but believe your tags are present, it might be that your system is overwhelmed with tag collisions. This is a result of the tag delay being too short for the number of tagged resident fish. Every transmission results in a collision and no (or very few) detections are recorded. In this case, you would need to lengthen your tag delay in future deployments in order to accommodate your expected fish residency. The VEMCO on-line collision calculator can help you select an appropriate tag delay.

If you have few Syncs and thus few Detects, but a high number of pings, you may be experiencing interfering noise either from a manmade source (i.e. boats, echo sounders, etc.) or from a biological source (i.e. snapping shrimp). In this case, you may need to deploy your receiver elsewhere. If you are working near a reef and the noise is biological, sometimes just moving the receiver away from the reef will improve this.

If you have few SYNCs or the number of Detects is well below your SYNCs and you believe there are only a handful of fish nearby (i.e. no collision activity suspected), you may have a bad echo situation. Long, strong echoes can cause interference even when only a single tag is present. In this case, the receiver almost certainly will need to be moved to improve performance but often by only a short distance. Proper range testing with a single controlled tag will help you determine if your receiver site is prone to echoes or other issues. A well placed sentinel tag with a long delay (approximately 10 minutes) can also be useful for monitoring the performance of your study.

Please note that the log information, described above, provides a qualitative analysis only and one should be careful to not try and draw specific conclusions through quantitative ratios of these values. We would normally suggest you review the logs in detail to give you direction on possible remedial actions only if the receiver did not seem to be performing well.

The VR2 receiver records these stats as single summations over the entire lifetime of your deployed study (between receiver initializations) while the VR2W records these on a daily basis. As such, the VR2 statistics are not as useful for diagnosing study set-up issues.

Q31 - How does VRAP software help me analyze/process/organize the data I collect?

VRAP Software V5.0 gives users the ability to process the true latitude and longitude position of tags. Users with latitude and longitude data on a scaled bitmap can determine a true world position for the tagged animal based on buoy position. Other features of the VRAP V5.0 software include:

• The ability to concatenate separate studies



• The ability to enable or disable individual tags at any point during a study



• Time referenced recordings, such as a note indicating when a noisy vessel entered the study area



• The ability to specify the period of time the system tracks an individual tag and the frequency of the data upload



• Adds way-points to a study



• Provides buoy status window with information on signal strength, battery voltage, receiver gain, time of last communication and tag status.

Q32 - How does VUE software help me analyze/process/organize the VR2 data I collect?

The VUE (VEMCO User Environment) software has been developed to aid researchers in gathering, viewing and analysing their acoustic detection data. VUE is not receiver centric but instead employs a central database to allow the user to collect and view data from multiple receivers of varying types. Using receiver plug-ins, VUE provides a receiver specific link which allows the user to communicate with the receiver to perform such functions as retrieving the receiver data files, setting the receiver clock, clearing the receiver memory, and changing the receiver code map.

VUE can create one or more central databases combining data files from multiple receivers and multiple types of receivers (i.e. VR2W and VR2). Legacy VR2 files and VR3-UWM datafiles can also be imported into the VUE database. Having a central database allows the user to easily compare detections from multiple studies, across multiple years and from varying locations if applicable.

You can download the software and the manual from the VUE Support Page.

Q33 - What test should I use to remove False Detections?

False detections (detection of a transmitter that is not actually present) are typically characterized by isolated occurrences of the ID in question - i.e. either a single detection (the most common situation) or successions widely separated in time (typically days or more apart). However, it is important to realize that the mechanisms that create false detections are not completely random and therefore, the occurrence of an ID more than once does not make the detection valid. You need to observe at least a pair of detections relatively close together to safely classify it as valid.

Analysis and simulations described elsewhere have shown that a safe test for validating detections at a single receiver is:

• At least one pair of detections less than 30 minutes apart



• More short intervals (i.e. pairs less than 30 minutes apart) than long (i.e. pairs 12 hours or more apart)

The 30 minute and 12 hour parameters above are somewhat arbitrary but have been shown to work well for average transmitter delays up to at least 3 minutes. For longer delays, one would relax the short criterion somewhat - say to 60 minutes for an average delay of 5 to 10 minutes.

See our Application Note on False Detections.

Q34 - Will the above test reject some valid detections?

The answer to this question is, in many cases, yes some valid detections will be rejected by the above test. The contrary is very possibly true as well - i.e. a false detection may pass the test. In this regard, it is important to realize that one can never develop a perfect test, therefore, the criteria for the test described above has been deliberately biased on the conservative side - i.e. rejecting a few valid detections. Automation of this First Scan Acceptance test leaves a very small number of questionable detections to analyze.

As an example, the above test was run on data files from a group of receivers experiencing a very high level of collisions and echoes - one of the most difficult situations we've seen. The three weakest detections accepted had the following characteristics:

All of these look acceptable. The table below shows the four strongest detections rejected.

With further analysis, it is very possible the first two would be accepted while ID #3 likely would not. There is virtually no argument for accepting the remaining rejected detections (not shown here).

See our Application Note on False Detections.

Q35 - Are there situations in which single or isolated detections can be accepted?

The fact that a detection is isolated does not guarantee that it is false so there is always an interest in trying to determine if it can be accepted. Since false detections are generated by one or both of:

• collisions between two or more transmissions, and/or
• extraneous pulses due to noise or long echoes (i.e. echoes lasting longer than the receiver's Blanking Interval)

then you can be reasonably safe in accepting them if you can show that neither of the above conditions exist.

See our Application Note on False Detections.

Q36 - I have detected a tag which does not belong to my project and is unknown to me. How do I identify the tag's owner?

This is an increasingly common occurrence as more and more compatible tags and receivers are deployed. Many of these detections will have significant scientific value and, therefore, we encourage users to follow the procedure we have set up to make the detection data available to the tag owner. This procedure takes into account a number of factors including the desire of some users to keep their data and tag IDs confidential and the possibility of the "foreign" detection being a false detection.

The following summarizes the procedure:

• Send an email to Customer Support listing the "foreign" IDs and the associated receiver logs (.VRL or legacy VR2 format) and indicating your willingness to share the detection data with the tag owner(s).
• VEMCO will use its internal tools to analyze the logs to verify that the detections are not false detections.
• For all positive detections, VEMCO will query its tag IDs database to determine the tag owner.
• The Tag owner will be contacted and, if he or she agrees, you will be supplied with contact information so that the relevant detection data can be exchanged. One convenient way to do this would be by exporting the relevant detections from VUE.

Please be assured that the receiver files you submit will be treated as confidential information.

Q37 - Can I use anti-oxidant marine paint to inhibit marine growth?

VEMCO receivers that are intended for long duration underwater deployments are made of materials that are resistant to adhesion of common underwater growth (barnacles, fungus, etc). If you choose to apply an antifouling coating to the receiver we suggest using ablative antifouling paint. These paints wear off over time. We recommend INTERLUX, MICRON CSC paint applied according to the manufacturer's instructions. Although VEMCO has not noted any significant degradation in performance of receivers with these coatings applied, results may vary.

Q38 - Can you customize your products to unique requirements?

Yes. We have always recognized the importance of working with customers to evolve our products so we welcome the opportunity to discuss new and more demanding requirements. Often, this leads to identification of enhancements or new products which are of value to a wide range of customers.