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| # | Post Title | Result Info | Date | User | Forum |
| Stacking waveform data (SEG2) files using Pickwin | 4 Relevance | 2 years ago | Gretchen Schmauder | Software | |
| Stacking waveform data (SEG2) files using Pickwin Make sure your dimension size is large enough. To start, select "option", then "Dimension size". If the maximum traces is smaller than the Total number of traces, increase the maximum traces, check “Change dimension size” and click “OK” to change dimension size. Open one waveform file as usual. Open another waveform file as usual. Choose “Append to present data”. If you want to change the color of traces depending on files, change component (2 to 10), check “Change” and click “OK”. Note that color does not affect stacking. Trace color is shown below. If you uncheck the “Change”, all traces are shown black. Confirm Total number of traces. Two waveform files are shown together. Make sure there is no time difference between shots. After importing 3rd file. After importing 4th file. Make sure there is no time difference among shots. Confirm Total number of traces.. All waveform files are shown together. Make sure there is no time difference among shots. Select “Processing”, “Vertical stack”. Select “a. Average” and click “OK”. You may select “Semblance” or “Semblance weighted stack” to emphasize coherent signal. Stacked data is shown. | |||||
| Thoughts on Attaching a Magnetometer to a non-Ferrous Sled or Frame | 3 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Regarding the deployment of magnetometers on conductive sleds or carts near power lines: Depending on the proximity of the magnetometer to the sled, elevated field readings may be observe under power lines are a result of AC induction in the aluminum sledge you are using as the tow vehicle. The reason there can be a DC effect from an AC source is due to 1) the strength and proximity of the induced AC source and 2) the orientation of the induced AC field relative to the Earth's field (DC). Our cesium-vapor magnetometers measure the Total local field continuously but report these measurements periodically, e.g at 10, 1000 times per second. For each reporting period, both the AC and DC components of the Total field are integrated to produce the measurement result as a time average over the measurement cycle. If your measurements are being reported 10 times per second (10 hz sample rate) and the AC component of the field is 50 hz, then each measurement will include exactly 5 AC cycles. This AC component will add to the DC component as a vector sum and the magnetometer will measure the magnitude of the resultant vector. Note that the vector component of the 50 hz AC field that is parallel to the DC component will not contribute to measurement results: for half of each AC cycle this field is greater than the DC field and for the other half of the cycle it is less than the DC field by an equal value. This is not the case for the AC vector component that is perpendicular to the DC field: it will be adding magnitude to the DC field on each 1/2 cycle to produce a half-wave-rectified wave form. Specifically, this rectified field will add to the DC field by an amount equal to about 35% of its peak-to-peak field strength in the direction perpendicular to the DC component. The AC rectification described above is only seen on close approach to very strong AC sources (high tension power lines). An aluminum sled can act as an indirect source of the AC fields: the radiated 50 hz field from the power lines is inducing 50 hz eddy currents in the sled and, if a magnetometer is in close proximity of the sled's aluminum plates, it will detect large AC field values. Note that surveying near other large, planar conductors under the high tension power line can produce a similar effect. These would include metal buildings, metal fences, and pipelines. We recommend constructing magnetometer sleds from non-conductive materials. If this is cannot be done, then conducive materials should be kept as far from the sensor as is practical and the sled's construction should not include sheets of conductive materials. Any joints between conductive structural elements should be insulated as well. You can use the magnetometer itself to measure the effect of the sled. | |||||
| MagStation is available | 2 Relevance | 6 months ago | Wei Jiang | News & Events | |
| MagStation, the new MFAM magnetometer base station is available. It's Geometrics’ latest and most advanced magnetometer base station, designed for high-sensitivity, stationary monitoring of the Earth’s Total magnetic field. Please see the product page for details. MagStation Magnetometer Base Station | |||||
| RE: Correct grounding technique for Geode seismographs | 2 Relevance | 1 year ago | Anton Yuriev | Hardware | |
| Thank you for detailed answer. I understood that common practice is separate grounding of each module. Also we will definitely try to shield each geophone with a separate ground, but this will require a large amount of preliminary work. Regarding 50 Hz filtering. We conducted a small experiment in the field to determine the frequencies of background electrical noise captured by geophones. Having set the minimum possible sampling period for Geod, I recorded 9 consecutive intervals (128 seconds each) of passive observations. This resulted in a Total of 19.2 minutes of continuous background noise recording at 125 Hz sampling rate. Then I calculated the signal spectrum from each geophone separately (19.2 minutes of recording), and then obtained the average spectrum for all sensors. For example, the figure in the appendix shows the average spectrum from 24 sensors (red curve) versus the spectrum of an individual geophone (blue curve). In general, I am interested in noise in the 30-50 Hz range. There are no clear peaks at 50 Hz on the frequency response graph. Peaks at 20, 25, 30 Hz are present constantly at any time of the day. In general, the frequency response of passive observation signals increases smoothly with a maximum around 48 Hz. I mean that filtering in some narrow frequency range in this case will not help much in my understanding. Thanks again for the advice. We’ll experiment. Attachment : 24 geophones 19.2 minutes 125 Hz sample rate.jpg | |||||
| RE: Geometrics preliminary MagArrow and MagEx data processing program download | 2 Relevance | 1 year ago | Ahmed Ramadan | Software | |
| Hello Dears, I'm new to Geometrics products and interested in MagArrow. I have some questions please. As a geophysicist, I examined the attached data and applied heading compensation to the measured data. My questions are after applying the 4th difference filter (the last panel in the attached figure) which is very important for measuring data noise especially comTing from the drone. I found the range to be very high and exceeding +/- 0.1, even after applying low pass filter to reduces the sampling rate of data from 20 Hz to 10 Hz. I think one of the biggest advantages of the MagArrow is that the sensor is suspended 3 meters below the drone to cancel out the effect of the noise coming from the drone, so I need to explain that. Attachment : 4th difference.jpg Secondly, in the attached file of the survey, the range of the Total magnetic field data is about 43,000 nanoTesla, while when calculating the IGRF for that region based on longitude and latitude, I found that the range is about 49,000 nT, which is very far from the measured data? Could you please explain to me the answers to these questions because our goal is to explore minerals and not UXO. Kind Regards, Ahmed | |||||
| Is it possible to extend the cables between the MFAM sensors and module? | 2 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| The cables between the sensors and the MFAM module are flexible circuit boards, and the length is limited to 20 inches. It is possible to remove the MFAM module from the Development kit box and then reconnect it using a ribbon cable. That would allow you to extend the MFAM module and sensors away from the Dev Kit box. Our engineers have tested it to 4 meters. Below are some details about the ribbon cable. The connector on the MFAM unit is Samtec FSH-110-04-F-DH. Its mating connector is Samtec SFMH-110-02-L-D-WT. The easiest option for an extender cable between the MFAM and the Dev Kit is a pair of cable assemblies from Samtec www.samtec.com which has male/female mass terminate connectors put onto a ribbon cable. These connectors plug directly into the MFAM I/O connector and also into the Development Kit. We are comfortable with lengths to 10 feet Total. The samtec P/N for this cable is: FFMD-10-T-60.00-01-F-N The ‘60.00’ number specifies the cable length in inches (which equals 5 feet). We have found that there is generally a 2-4 week lead, time since they are made to order and not an off-the-shelf part. (There is another solution as well if you want to make adapter boards at each end (Dev Kit and MFAM). The exact Samtec mates for the MFAM / Dev Kit connectors are made in PCB mount connectors only, so if you make simple small adapter board to adapt the samtec connector to another connector of your choice. We've done this with ExpressPCB which is fast and inexpensive. A board set from ExpressPCB is about $70 including shipping. Our Engineering Team has a design and parts list they can send you if you're interested in going this route.) | |||||
| How many channels do I need for Seismic Reflection surveying? | 2 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| There is no one right answer to this question. The higher the channel count, the higher the fold (for any given shot interval), and the higher the signal/noise ratio. For land seismic, we generally recommend 24 or higher-fold data. If the shot spacing is equal to the geophone spacing (typical), this means that you must record on at least 48 channels with each shot. In addition, you must have extra channels for electronic rolling. Taken together, this means that for land CDP reflection, you should have a minimum of 72 channels, which will allow you to roll 48 live channels through a Total of 72. | |||||
| Understand Dead-zone, Heading Error, and their importance for the MagArrow | 2 Relevance | 2 years ago | Gretchen Schmauder | Application | |
| Dead-Zones The MagArrow is a dual sensor magnetometer powered by MFAM sensors, but it is configured for use so it only has a single data output. The reason Geometrics has done this is so we could ensure the MagArrow encounters no "dead-zones". A dead-zone occurs when the orientation of a magnetometer results in the magnetometer producing poor or no measurements. The dead-zone angle depends on the location of survey. Since we have the two MagArrow MFAM sensors in orthogonal orientations, the MagArrow Magnetometer has operability worldwide without affecting survey orientation, making it much easier to use for the customer. Heading Errors Heading errors are a type of noise magnetometers can experience. They come from three sources: Sensor Console Operator Magnetic materials in the sensor itself are the primary cause of heading errors. The physics of Cesium and Potassium magnetometers can contribute small amounts to the Total heading error. Magnetic contamination near the sensors, operating electronics, or operator can all contribute to heading error. Heading errors look like herringbone patterns in survey images. Alternate lines can also be corrugated. Dead-Zones vs Heading Errors while these two sources of error in magnetic data are different, there is overlap between them when operating a magnetometer like the MagArrow. Heading errors can be fixed relatively easily in software, where dead zones can be much harder to manage. If a line is completely ruined because of a dead zone then they will need to re-fly the line/mission which is time consuming. Even with advanced users, these sorts of mishaps can happen. Additionally, the closer a mag sensor operates to a dead-zone, the larger a heading error will be measured. With compensation software and a pre-survey heading error flight, heading error can be reduced dramatically to around 1 nT for the MagArrow. Click to view the difference between Raw and Processed MagArrow Data The MagArrow is only outputting a single value as a means to create a “no-dead-zone” system. Obviously each sensor has a dead zone themselves, but with the sensors orientated orthogonally at least one sensor at all times will have a magnetic measurement. By combining the measurements from both sensors it is possible to generate a constant magnetic field measurement independent of orientation and location in the world. If the data from each MFAM sensor in the MagArrow was individually reported there would be gaps in the mag fields observed by either sensor as you fly, rotate, and swing. | |||||
| Do Cesium Vapor Magnetometers Require Calibration | 2 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Our cesium-vapor magnetometers do not require periodic calibration in order to maintain the accuracy as described in our published specification when the instrument is operated within specified environmental ranges. Geometrics cesium-vapor magnetometers are manufactured and tested based on the discoveries and the basic designs of Carian Associates (U.S. Patent 3,071,721). This method of Total magnetic field measurement relies upon the measurement of the optical absorption of a particular cesium spectral frequency by the cesium vapor enclosed in a small glass cell. This method is similar to those used in the measurement of atomic emission and absorption frequencies using spectroscopic reference cells. The technique thus relies on well-known fundamental quantum mechanical constants for accurate and precise measurement of the magnetic field. As a result, no adjustments to the sensor are needed in order to correct or maintain its accuracy and Geometrics sensor and sensor driver electronics are designed to either work correctly or to not work at all and to report both the strength of the magnetic field as well as the strength of the electrical signal produced by the working sensor. In this way, the signal strength measurement provides a direct indication of the operational state of the magnetometer while it is running and serves to alert the operator if the magnetometer encounters environmental conditions that are outside of its operating range. Occasional maintenance of the instrument at Geometrics facility should be performed when the instrument's internal diagnostics indicate substandard performance as described in the operator's manual. Please contact Geometrics Support for technical advice and additional information pertaining to your specific model. | |||||
| Battery percentage and status | 2 Relevance | 2 years ago | Magnetics SW | MagEX | |
| Overview The MagEx instrument and the MagNav app both display information about the state of the instrument's battery. Battery state and reporting exist in bands according to percentage of remaining battery capacity: 30% or higher:The instrument has good remaining capacity.The LED on the instrument's power switch glows a solid green.MagNav displays the battery percentage or voltage in black text on a white background. Between 20% and 30%:The instrument has capacity to survey for additional time, but if you will be surveying a significant amount more, start thinking about changing the battery.The LED on the power switch is blue.MagNav displays the battery percentage with a blue background. Between 5% and 20%:You can continue to survey, but the battery is running low and you should consider changing the battery soon.The LED on the power switch is red.MagNav displays the battery percentage with a red background, and periodically notifies you that the battery is running low. Below 5%:The battery is running low, and the instrument may turn off at any time in order to preserve battery health. You should change the battery as soon as possible. Temperature-related effects:Battery performance also changes as the temperature of the battery changes; as the temperature of a battery falls, the voltage it supplies also decreases, and the Total energysupplied by the battery decreases. This means that in cold weather a battery will not last as long as in hot weather. The battery percentages reported in the instrument are adjusted for the effect of temperature; at a given battery voltage a cold battery will display a higher percentage than a warm battery will report. The effects of colder temperatures are not normally permanent; as a battery warms up, its output voltage and energy return to higher levels. Notes about the calculation:The MagEx instrument includes 2 batteries, and each battery includes 3 separate cells. Battery percentages are calculated from only one battery in the instrument - either the single battery if only one is connected, or from the better battery if two batteries are connected. Reported battery percentage is an estimate, based on measurements of the behavior of healthy batteries in instruments in the field and in the lab. Battery performance may change as a battery ages and as the temperature changes. The best practice for batteries is to use 2 healthy, fully charged batteries, and replace them both when the percentage falls below 20%. | |||||
| Differences Between our Standard Cesium Magnetometers and the SX Model | 2 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Clarification regarding Geometrics standard magnetometers SX versions and the US Govt. export regulations In this brief review magnetometer specifications are given in terms of both nT/sq-rt-Hz RMS and in Peak-to-Peak (P-P) noise values as both forms are often used to describe instrument performance. The US Government specifies that an export license is required for magnetometers that have a sensitivity of better than (noise level less than) 0.02nT/sq-rt-Hz RMS. Obtaining an export license is not difficult but it does require approximately 6-8 weeks. Not all geophysical applications require export license sensitivity and so we offer SX models that have a noise floor of 0.02nT/sq-rt-Hz RMS. Compare this with our G-858 Magnetometer at 0.008nT/sq-rt-Hz RMS and our G-882 Marine Magnetometer at 0.004nT/sq-rt-Hz RMS. What does SX performance mean in the survey results? When the sensor is deployed at some distance from the “source” such as in above the shoulder mounting for geological surveys (G-859SX) or at some distance (several meters) from the seafloor for G-882SX surveys, the distance from the source provides some natural filtering of the near surface response. This means that surveys not focused on small target detection (20mm ordnance rounds) where the sensor is deployed very close to the ground (<1m), SX performance is more than adequate. Let us consider the G-858 man-portable model. Under low noise laboratory conditions at a sample rate of 10 samples per second, the G-858SX will show approximately 0.125 nT of noise (peak-to-peak) compared to a standard G-858 of about 0.05nT P-P. To understand the significance of this, the natural earth background noise due to geomagnetic micro-pulsations is about 0.02nT/sq-rt-Hz (about 0.125 nT peak-to-peak) at the quietest of times. Micro-pulsation amplitudes of 1 or 2 nT are common and, during active periods, they may be larger than 10 nT. Any magnetometer will produce a record of the combination of the background noise (micro-pulsations, diurnal drifts, etc) and its own internal noise. If the various noise components are not correlated with each other they will add as the square root of the sum of their squared amplitudes. In the case of the G-858SX, the combination of instrument noise and background micro-pulsations will be: √(0.125nT^2 + 0.125^2) = 0.18nT. For the standard G-858, this combination will be: √(0.05nT^2 + 0.125^2) = 0.13nT. That is, the SX model will exhibit about 30% more noise amplitude compared to the standard model if the atmospheric noise is typical. Unless the survey measurements are referenced to a high performance base station magnetometer equipped with a very accurate clock, the user will not be able to detect any difference between SX and standard performance. If such base station data were available, the greatest difference that would be seen should be no greater than about 0.05nT P-P in the average peak-to-peak amplitude. Such small differences cannot be seen or even detected in the Total field contour maps made for exploration surveys which are typically contoured at 1nT or more. It should be remembered that the amplitude of the geomagnetic micro-pulsations in the frequency range from 5hz to 10hz is not constant; i.e., at most times they will be greater than 0.125nT and occasionally less than this value. Their intensity is governed by the average intensity of the instantaneous global thunderstorm activity and sunspot activity. | |||||
| What are the differences between the standard MFAM and the SX version? | 2 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| The only difference between the standard and SX version is the sensitivity is 4pT/rt-Hz and 20 pT/rt-Hz respectively. Here is an expected response with the magnetometer moving past a generic magnetic projectile: In this case the amplitude is about 1nT in Total from peak to peak. The feature itself is quite distinguishable. This is assuming there is no noise in the system. Here is what the data looks like with 4pT/rt-Hz noise: You can see the general structure is still there but there is a little more wiggle on the trace that is associated with the noise of the system. Here is the data with 20 pT/rt-Hz noise: Again, here the structure is clearly visible but the data looks a bit noisier. With some signal processing technique, such as low pass filtering, noises can be further reduced. Please note that in real surveys, detecting 1nT peak-peak anomalies is always a big challenge even with the most sensitive magnetometers due to other noise sources, such as motion noises and environmental noises. Therefore, SX version is in general NOT the limiting factor for conducting surveys. To understand this concept better, you can use the magnetic gradient tool developed by our partner in the UK, Geomatrix Earth Science. | |||||
| Why do we see less structures in MagArrow surveys, compared with land magnetometer surveys? | 2 Relevance | 2 years ago | Rui Zhang | General Magnetometer Info | |
| This is most likely due to the fact that land surveys are typically much closer to the ground (therefore closer to targets). Two spatially separated magnetic anomalies can be resolved on the ground but not several meters above the ground, as shown in the simulation plot below. The simulation is for two targets, separated by 4m, located at z= -2m, y=3m, x= 0m and z=-2m, y=7m, x=0m. The Total magnetic signal on the x=0 plane from the two targets are plotted in 2D as a function of y and z (with z=0 being on the ground). For land magnetometer surveys, z = 0.5m or less. If we draw a line at z = 0.5m (survey line), it is clear that there will be 2 peaks in the sensor reading along y direction as long as the magnetometer has a high enough sample rate. Therefore, the two targets can be resolved. For MagArrow surveys, if the above ground level (AGL) is >3m, the two targets cannot be resolved no matter how high the sample rate is. This simulation also indicates a rule of thumb about the linespacing in MagArrow surveys. The linespacing should be about 1-2 times the AGL. Less than the AGL will not produce any higher resolution map. The simulation plot provides customers with a general idea of how fast the magnetic signal decays as a function of distance from the target. The signal falls as 1/R^3. | |||||
| What are the differences between the standard MFAM and SX Versions | 2 Relevance | 2 years ago | Gretchen Schmauder | MFAM | |
| The only difference between the standard and SX version is the sensitivity is 4pT/rt-Hz and 20 pT/rt-Hz respectively. Here is an expected response with the magnetometer moving past a generic magnetic projectile: In this case the amplitude is about 2nT in Total from peak to peak. The feature itself is quite distinguishable. This is assuming there is no noise in the system. Here is what the data looks like with 4pT/rt-Hz noise: You can see the general structure is still there but there is a little more wiggle on the trace that is associated with the noise of the system. Here is the data with 20 pT/rt-Hz noise: Again, here the structure is generally there but the data looks quite a bit noisier. So for smaller targets or more subtle anomalies they can be obscured or missed entirely. To understand this concept better, you can use the magnetic gradient tool developed by our partner in the UK, Geomatrix Earth Science. | |||||
| How Far Can a Magnetometer 'See'? | 2 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Total field magnetometers like the optically pumped cesium magnetometer are passive devices, they do not send out waves or pulses. They measure distortions in the earth’s normally homogenous magnetic field and can sense distortions due to ferrous objects at great distances. The basic rule of thumb is that one ton (1000 Kg) of steel or iron will give us a 1nT anomaly at 100 ft. or 30m. Since the amount of distortion falls off as the cube with distance (compare a metal detector which falls off as the inverse 6th power!) and is linear with mass, every time we cut the distance in half, we can see 1/8th the mass. Therefore, we can sense 250 lbs. (100kg) at 50 feet (15m), or 30lbs (15kg) at 25 feet (8m), or 4lbs (2kg) at 12 feet (4m). However this is not the whole story. The factors given above are for induced magnetic fields only. Many targets also have remnant or permanent magnetic effects (meaning they have become magnetized either in production or by the earth’s field) and can therefore have larger anomalies by a factor of 3 or 5 or more. Also many hollow objects like barrels or other tubular structures appear as though they are solid due to self-shielding from the earth’s field, and thus have much larger anomalies than their mass would predict alone. Pipes fall off as the inverse square and are thus detectable at even greater distances. Please see our Applications Manual for Portable Magnetometers for more information. | |||||
