قاموس مصطلحات GPR
| المصطلح | الرمز الشائع | الوحدات النموذجية | الوصف |
|---|---|---|---|
| عرض النطاق 3 ديسيبل | ميغاهرتز أو جيجاهرتز | نطاق الطيف الترددي الذي يظل فيه سعة إشارة GPR أعلى من قيمة تساوي (السعة القصوى /√2) | |
| عرض ثلاثي الأبعاد | المصطلح المستخدم عند عرض البيانات التي تغطي منطقة سطحية مع البُعد الثالث الذي يمثل الوقت أو العمق أو الوقت. يتم تجميع البيانات في وحدات الحجم (voxels) الصغيرة ويتم عرض قيم البيانات باستخدام أدوات عرض الحجم التي تعرض شرائح مقطع عرضي أو شفافية متغيرة لحجم البيانات الثلاثية الأبعاد. | ||
| عرض النطاق 6 ديسيبل | ميغاهرتز أو جيجاهرتز | نطاق الطيف الترددي الذي يظل فيه سعة إشارة GPR أعلى من قيمة تساوي (السعة القصوى /2) | |
| وضع الاستحواذ | مصطلح يُستخدم لوصف الطريقة التي يتم بها بدء استحواذ آثار GPR. الطرق الشائعة هي: المسافة - يتم جمع الآثار في مواقع مكانية (عادة خطوات متساوية المسافة) ويُحدد الموقع باستخدام عداد المسافات أو جهاز قياس المسافة الآخر. التشغيل الحر - يتم جمع الآثار واحدة تلو الأخرى بأسرع ما يسمح به النظام. الوقت - يتم التحكم في جمع الآثار بواسطة فاصل زمني محدد إما بين الآثار أو زمن التأخير بعد الانتهاء من جمع الأثر السابق. الزناد الخارجي - يتم التحكم في جمع الآثار بواسطة زناد خارجي مثل الضغط على الأزرار يدويًا أو الإشارة الإلكترونية المدخلة. | ||
| الركام | أي مادة معدنية صلبة وغير قابلة للتفاعل تُستخدم للخلط في قطع مقطعة حسب الحجم. وتشمل الرمال، الحصى، الحجر المكسر أو الخَبَث. المواد التي تُستخدم عادة في إنشاء الخرسانة أو الأسفلت. | ||
| موجات الهواء | تنبعث أنظمة GPR من طاقة الترددات الراديوية التي تنتقل في جميع الاتجاهات من المرسل ويتم استقبالها من جميع الاتجاهات بواسطة المستقبل. يُستخدم GPR لاكتشاف الإشارات تحت السطحية. الإشارات التي تنتقل عبر الهواء فوق الأرض وتنعكس من الأشياء فوق الأرض تنتج إشارات تشويش غير مرغوب فيها تُسمى موجات الهواء. | ||
| الهوائي | جهاز يُستخدم لتحويل الإشارات الكهربائية إلى موجات كهرومغناطيسية منتشرة. في GPR، عادة ما يكون هناك هوائي مرسل وآخر مستقبل. عند دمجه مع الإلكترونيات المرسلة أو المستقبلة، يُستخدم مصطلح المحول (انظر المحول). | ||
| فصل الهوائيات | عادة ما يستخدم GPR هوائيات منفصلة للإرسال والاستقبال. المسافة الخطية بين المركز الفعلي للهوائيات يُشار إليها بفصل الهوائيات. | ||
| مجموعة | المصطلح المستخدم في أنظمة GPR المتقدمة التي تحتوي على مجموعة من الهوائيات المرسلة والمستقبلة المنتشرة عبر حجم مكاني مع مواقع مكانية ثابتة مُحددة لكل عنصر. | ||
| الانخفاض | α | نيبرز أو ديسيبل/متر | المصطلح المستخدم للإشارة إلى تقليل سعة الإشارة لإشارة مارة نتيجة لانخفاض الطاقة في الوسط. بالنسبة لـ GPR، يرتبط التوهين عادةً بالموصلية الكهربائية للوسط. |
| التحكم التلقائي في المكاسب | AGC | وظيفة مكاسب تحاول توحيد سعات جميع إشارات GPR من خلال تطبيق مكسب عكسي يتناسب مع قوة الإشارة. يُعد هذا النوع من المكاسب مفيدًا بشكل خاص لتعريف استمرارية الأحداث العاكسة. | |
| طيف التردد المتوسط | AFS | مصطلح يُستخدم لوصف عملية حساب ثم متوسط جميع أطياف السعة للآثار في ملف أو قسم بيانات GPR. يُظهر الرسم البياني محتوى التردد للإشارة، وبالتالي يُستخدم بشكل شائع لتحديد معلمات التصفية الترددية، مثل تطبيق مرشح نطاق تمرير. | |
| سعة الأثر المتوسطة | ATA | رسم بياني يُعرض فيه متوسط السعات المربعة لإشارة GPR على طول خط GPR بالكامل. أثبت هذا الرسم البياني كفاءة كبيرة في عرض كيفية انكماش سعة إشارة GPR بسرعة، وتقييم مستويات الضوضاء المحيطة، مما يوفر فكرة عن الحد الأقصى لعمق اختراق الإشارة. | |
| طرح المتوسط الخلفي | BAS | عملية حساب المتوسط لجميع الآثار في مجموعة بيانات GPR ثم طرح هذا الأثر المتوسط من جميع الآثار في مجموعة البيانات. يُستخدم غالبًا في بيانات GPR منخفضة الجودة لقمع الضوضاء المتماسكة التي تظهر كحزم ثابتة في صورة GPR. تجعل هذه العملية الأحداث الأضعف والمتغيرة مكانيًا (مثل القباب الناتجة عن الأهداف النقطية) أكثر وضوحًا عن طريق إزالة الاستجابات الزمنية الثابتة المشتركة لجميع الآثار في خط GPR. كما يُستخدم أيضًا لإزالة موجات الهواء المباشرة وموجات الأرض المباشرة (نبض الإرسال) الظاهرة عند الزمن صفر في بداية الخط التي تكون تقريبًا ثابتة في بيانات الاستطلاع ذات الإزاحة المشتركة. | |
| طرح الخلفية | BSUB | هذه العملية مشابهة لطرح المتوسط الخلفي ولكنها تستخدم المتوسط المتحرك على مجموعة محلية من الآثار المركزية على الأثر المعالج المحدد للحصول على الأثر الخلفي المتوسط للطرح. تعزز هذه العملية الأحداث المحلية (مثل القباب الناتجة عن الأهداف النقطية) وتُخمد الأحداث الأفقية أو المتغيرة ببطء. يمكن أن تكون هذه الطريقة مفيدة جدًا لإزالة الأحداث المسطحة المحلية. كما يُستخدم أيضًا لقمع موجات الهواء المباشرة وموجات الأرض المباشرة (نبض الإرسال) الظاهرة عند الزمن صفر في الأثر؛ بداية الخط التي تكون ثابتة في بيانات الاستطلاع ذات الإزاحة المشتركة. | |
| مرشح نطاق تمرير | العملية التي يتم فيها الاحتفاظ بمجموعة من الترددات في بيانات GPR، بينما يتم قمع الترددات الأخرى. أجهزة GPR هي أجهزة تسجيل نطاق عريض جدًا ويمكن أن تحتوي على إشارات ضوضاء لم تُنتجها المرسل. يمكن أن يُحسن اختيار الترددات التي يجب الاحتفاظ بها وقمعها من قابلية تفسير صور GPR. يتم تحقيق تصفية النطاق التمرير في الغالب عن طريق التحليل الفورييه ووزن الطيف، ولكن يمكن أيضًا تحقيقها بواسطة الالتفاف الزمني لإشارة GPR مع استجابة مرشح زمني مناسب. | ||
| عرض النطاق الترددي | نطاق الترددات التي يتم خلالها إرسال أو استقبال الإشارة بواسطة جهاز معين فوق سعة أو قدرة محددة. | ||
| التردد المركزي | مصطلح مُحدد للأجهزة ذات النطاق العريض للغاية. يتم تعريف حدين علوي وسفلي من حيث سعة الإشارة (مثل عرض النطاق 3 ديسيبل). يُعرف المتوسط بين الترددين العلوي والسفلي على أنه التردد المركزي. غالبًا ما يكون التردد المركزي قريبًا جدًا من التردد الذي يصل فيه سعة الطيف إلى ذروتها في أنظمة GPR. نتيجة لذلك، يُستخدم مصطلح التردد الأقصى والتردد المركزي بشكل متبادل، على الرغم من أن هذا ليس دقيقًا تمامًا. | ||
| القناة | المصطلح الذي يُستخدم لوصف إشارة GPR التي يتم إنشاؤها بواسطة زوج واحد من هوائيات TX-RX التي لها معلمات ثابتة مثل التردد والفصل والتوجيه، وما إلى ذلك. (انظر أيضًا تعريف العنصر المصفوفة). | ||
| شريط الألوان | شريط من الألوان يعرض لوحة الألوان وغالبًا ما يتم تسميته لإظهار نطاق قيم البيانات (عادة سعات إشارة GPR) التي تمثلها الألوان المحددة في الصورة الملونة. | ||
| لوحة الألوان | المصطلح الذي يُستخدم للإشارة إلى تطابق قيمة البيانات مع اللون. يُشار إليها أحيانًا باسم جدول الألوان. غالبًا ما يُستخدم في GPR لتعيين قيمة سمة البيانات (مثل السعة) إلى لون في إنشاء المقاطع العرضية، وشرائح العمق أو الزمن، وصور ثلاثية الأبعاد. | ||
| نقطة المنتصف المشتركة | CMP | نقطة المنتصف المشتركة (CMP) هي نوع من أنواع مسح GPR حيث يتم تغيير مواقع هوائي المرسل والمستقبل، ولكن يتم تنفيذ الحركة بطريقة تجعل النقطة الوسطى ثابتة. | |
| تكوين الانعكاس ذو الإزاحة المشتركة | COR | المصطلح المستخدم عند جمع البيانات مع هندسة هوائي ثابتة يتم تحريكها من موقع إلى موقع. غالبًا ما يتم تثبيت كل من التوجيه والمسافة بين هوائي المرسل والمستقبل. انظر أيضًا إلى استقصاء الخط. | |
| تشغيل المستقبل المتزامن | المصطلح المستخدم عندما يقوم العديد من المستقبلات بجمع عينات البيانات في نفس الوقت. يتم تزامن جمع البيانات بحيث تجمع جميع المستقبلات البيانات في نفس الوقت بعد إصدار نبضة واحدة من المرسل. يجب أن تكون دقة توقيت المستقبلات الفردية في حدود عشرات البيكوثواني لتحقيق جمع بيانات ناجح. هذا يسرع بشكل كبير من جمع بيانات GPR مقارنةً بالتشغيل التاريخي للمستقبلات المتعددة. | ||
| الموصلية | σ | ميلي سيمنز/متر أو mS/m أو ميليموس/م (تاريخي) | قدرة المادة على توصيل التيار الكهربائي. في المواد المتجانسة، هذه هي معكوس المقاومة. يُسمى أحيانًا الموصلية المحددة. |
| المقطع العرضي | صورة ناتجة عن العرض الجانبي لعدد من الآثار التي تكون من مواقع قياس متجاورة. | ||
| الديسيبل | dB | الوحدة المستخدمة في التعبير عن نسبة في شكل 20 لوغاريتم 10 من النسبة. النسبة 10 تعادل 20 ديسيبل. | |
| المكاسب المتغيرة مع العمق | المصطلح المستخدم لمعامل ضرب يتغير مع العمق ويتم ضربه في الأثر. الهدف هو تغيير سعة الإشارة النسبية بالنسبة للعمق. انظر أيضًا المكاسب المتغيرة مع الوقت. | ||
| صورة العمق أو القسم | المصطلح المستخدم عندما يتم رسم آثار بيانات GPR جنبًا إلى جنب لإنشاء صورة للأرض حيث يكون المحور العمودي هو العمق، وغالبًا ما يتم الحصول عليه عن طريق تحويل وقت سفر الإشارة إلى عمق. غالبًا ما يتم اختصار المصطلح إلى "القسم" أو "صورة العمق". | ||
| شريحة العمق (صورة) | المصطلح المستخدم لوصف الصورة التي تم الحصول عليها عن طريق إنشاء شريحة عبر حجم البيانات كعرض بالألوان أو خطوط كونتور. يتم إنشاؤها عادةً بواسطة عملية حاسوبية. عادةً ما يتم اختصار المصطلح إلى "شريحة العمق". | ||
| إزالة الويّو | عملية إزالة المكون ذو التردد المنخفض جدًا من بيانات GPR. هذه المكونات منخفضة التردد ترتبط إما بالظواهر التحريضية أو حدود النطاق الديناميكي للأجهزة المحتملة. تتقلب قاعدة أثر GPR ببطء صعودًا وهبوطًا؛ في الأيام الأولى من GPR، كان يُطلق على هذا "ويّو". وأصبحت إزالة هذا التأثير تُسمى "إزالة الويّو". | ||
| dielectric constant | K | See dielectric permittivity. | |
| dielectric permittivity | K | A fundamental physical property that describes the electrical polarizability of a material. Free space or vacuum has a permittivity of 8.89 x10-12 Fd/m. Most often the term is applied to the relative dielectric permittivity where the material permittivity is divided by the free space permittivity. Most natural materials have a relative permittivity in the range of 1 -80 in the radio frequency range. The dielectric permittivity is often referred to as relative permittivity or dielectric constant. | |
| display unit | The term applied to a device that controls, records and displays the GPR data. This device is sometimes a personal computer (PC) but can also be a custom-built, fit-for-purpose computer system (see digital video logger DVL). | ||
| distance measuring instrument | DMI | A device for accurately measuring elapsed distances along a survey line or transect. The term is common in roadway surveys to measure longitudinal distance from an intersection or other visible geographic location. See also odometer. In GPR applications the output of the device may be used to trigger the acquisition of GPR at fixed distance (step) intervals. | |
| DynaQ | DynaQ | is an advanced, GPRLine-patented technology that dynamically adjusts stacking as system movement speed varies. Stacking is a means of improving signal to noise so being able to adapt the stacking to sensor movement speed creates a dynamic quality data acquisition technique. | |
| electromagnetic | EM | is the term applied to methods which use electric and magnetic fields to transmit signals or make sensing observations. The term is a general one that encompasses the whole field of science involved in electric and magnetic fields – particularly when the fields are time varying and therefore coupled. | |
| envelope | formed from a pair of traces that uniquely bracket the extremes of an oscillatory signal. The signal is assumed to have a zero average or base line, so the upper and lower traces are identical but of opposite sign. The envelope is obtained by using the method referred to as the Hilbert transform to calculate the positive and negative traces; the positive bounding trace is normally referred to as ‘the envelope’. The envelope does not have the oscillatory nature of the original signal. The envelope is more indicate of the data resolution. Enveloping can also simplify the GPR section display making it easier to interpret. Creating depth slices of the envelope is a powerful way of displaying GPR data that cover an area. | ||
| falling weight deflectometer | FWD | A non-destructive testing device that is used to perform structural testing for pavement rehabilitation projects, research, and pavement structure failure detection. It is used for conventional and deep-strength flexible, composite and rigid pavement structures. The FWD applies a dynamic load to the pavement surface, similar in magnitude and duration to that of a single heavy moving wheel load. The response of the pavement system is measured in terms of vertical deformation, or deflection, using seismometers. | |
| file size | bytes | The actual or physical limit on the amount of data stored in a computer file. | |
| first break time | Time of onset of the direct air signal at the GPR receiver, referenced to the start time of trace recoding. When plotting GPR data this time offset establishes the zero point on the time scale axis. In practice, this offset time on a GPR trace is determined by sensing when the receiver signal rises above a defined level for the first time from start of recording. | ||
| frequency | f | Hz, MHz, GHz | is the term applied when a signal is repetitive at regular intervals of time. Frequency measures the number of repetitions that occur in a time interval such as pulse per second or cycles per second. (Frequency can also be used in other contexts such as spatial frequency which indicates a signal that repeats with distance or length such as cycles per meter). The term is also used to indicate the center or peak frequency of a GPR antenna response although it is somewhat a mis-use of the term. |
| Fresnel zone | For a reflection from a surface, there is a finite area on the surface for which signals travelling from the source to the receiver are indistinguishable based on the time of travel or length of travel path. This area is defined to be the Fresnel zone or zone of influence. The Fresnel zone is defined by differences in path length being a faction of the wavelength when the signal is sinusoidal excitation. The zone of influence is the same concept but expressed in terms of differences in travel time being less than a fraction of the pulse-width of an impulsive transient signal. | ||
| gain | Process of amplifying signals to match recording device or the dynamic range of the display. See time gain. | ||
| global positioning system | GPS | GPS is a satellite-based approach to obtaining georeferenced coordinates. The satellites transit a defined timing signal and the GPR receiver, usually on or near the Earth’s surface, records the signals from many satellites and uses the signals to triangulate the best estimate of the receiver location in 3D space with reference to a standard earth geoid shape. The result is normally latitude and longitude and elevation as well as a very precise time. | |
| GPS Files | When GPS is used with GPR, the GPS receiver data is recorded in a data file and recorded information tied to the GPR data. When the GPS record is available and synced to the GPR data, Latitude and Longitude, UTM coordinates, and GPS elevation can be provided for every GPR trace in a data set. A GPS file is created by attaching a GPS system to the GPR system during data collection. GPS files contain lines of standard GPS positional output text (called NMEA strings) and the associated GPR trace number. When the GPS file is attached, latitude, longitude, and GPS elevations for every GPR trace can be saved into the GPR file. | ||
| GPZ | .gpz | A .gpz file is a GPRLine standard data file for GPR data recording and interchange. The .gpz is used with the PC-based GPR software called EKKO_Project. The .gpz file contains a wide variety of data files including GPS files and .dt1 GPR data files as well as proprietary data from GPRLine instruments and auxiliary sensors. | |
| Grid | A square or rectilinear set of straight lines which cover an area. Acquiring data on a grid means acquiring data along each line forming the grid. Acquiring data on a grid at regular spatial steps is the optimal way to obtain a data set suitable for advance signal processing, such as the creation of 3D volume renderings and depth or time slice images. Conventional notation is to use a first quadrant Cartesian coordinate system with X and Y axes. | ||
| Grid Resolution | is the term used to describe the XY spatial resolution attained in a grid and is controlled by the largest line or trace spacing. | ||
| grid size | term used to describe a real extent of a rectilinear grid (i.e. 5m x 10m, 20ft x 50ft., 24″ x 24″, 600 mm x 600mm). | ||
| grid survey | is the term to describe the process of acquiring data on a grid over an area with the end goal to create 3D, depth or time slice images. | ||
| ground-penetrating radar | GPR | Ground penetrating radar is a geophysical method for mapping subsurface structure using electromagnetic energy. There are several deployment methods, but all approaches involve a transmitter creating radio frequency signals typically in the 1 to 5000 MHz frequency range and a receiver which detects similar signals. The goal is to measure the impulse response or the transfer function of the surrounding medium with the view of reconstructing the material property structure. In its simplest form, a GPR system with a transmitter and receiver are moved over the ground surface and reflections returning from subsurface objects are detected, recorded and displayed to the user. | |
| herring bone effect | Term applied to distortion in a map image derived from a grid survey when there are measurement system errors. The effect is most pronounced when data are collected in alternating directions along grid lines with an improperly calibrated odometer. In the case of GPS or similar positioning techniques, the systematic positioning error can be created by a finite temporal response lag so that the measured response is delayed with respect to the device (GPR system) position. | ||
| horizontal stretch | A term used to describe stretching the horizontal (position) axis of a cross-section image. If GPR data positioning is distorted, this is a means of regularizing the spatial position so that distance is a linear-axes on a GPR cross section image. Sometimes the process is referred to as rubber banding or rubber sheeting since the effect is to stretch or squeeze the spatial axis of the data is achieve uniform spatial presentation. | ||
| hyperbola | Characteristic inverted “U” GPR response from a point target. (Mathematical form of the position-travel time response from a point target). The apex of the hyperbola (top of the inverted U) represents the location of the GPR system’s closest approach to the object. | ||
| hyperbola velocity estimate | A point source GPR refection appears as a hyperbola in the cross-section image. One of the parameters controlling the shape of the hyperbola is the ground velocity. Hyperbolic fitting enables the ground velocity and target depth to be estimated. | ||
| hyperbolic fitting | Process of fitting a hyperbolic shape to a local GPR response in the space-time domain. The fitting process yields a velocity estimate for the material (media) above the target and a depth estimate of the target. | ||
| lateral resolution length | The minimum lateral separation between two objects required so a GPR clearly detects two side-by side responses. | ||
| Line Profiling or Common-offset profiling | is the term to describe collecting data along one or more GPR lines for immediate site assessment using cross-section images. A series of lines can be used to help define site conditions prior to a grid survey. Also see Common Offset Reflection (COR). | ||
| Line | is the term used to identify the location of a single GPR data set. A line is normally straight, and data are recorded from the start to the end of the line. | ||
| Lowpass Filter | removes frequencies above a cut-off frequency – useful for removing high frequency noise in GPR data. The filter can be a zero-phase or causal type filter. It can be applied in the frequency domain via Fourier methods or in the time domain by convolution. | ||
| magnetic permeability | u | A fundamental physical property that describes the magnetic polarizability of a material. Free space or vacuum has a permittivity of 12.57 x10-7 H/m. Most often the term is applied to the relative permeability where the material permeability is divided by the free space permittivity. Most natural materials have a relative permeability. For most materials relative permeability is in the range of 1 +/- .00001 in the radio frequency range. For this reason, permeability has no impact on GPR signals. | |
| Megahertz | MHz | A measure of frequency equal to 1 million repetitions per second. See frequency. | |
| microsecond | microsecond =10-6s = 1000ns; occasional unit of GPR time. | ||
| Migration | The process of collapsing the response of a point target back to the source point. Common term in reflection seismic and similar to synthetic aperture image reconstruction. Can be visualized by thinking of the signal on a hyperbolic response being summed and placed at the apex of the hyperbola. | ||
| multiplex: | the process of creating a single stream of data obtained from a multiplicity of receivers or detectors. (The sequencing is normally fixed- i.e. for four channels named 1, 2, 3, and 4, the sequence of the samples in this serial stream might be … 1a, 3a, 2a, 4a, 1b, 3b, 2b, 4b, 1c, 3c, 2c, 4c, where a, b, c refers to each cycle of selected channels…) | ||
| multi-polarization configuration (multi-polarization): | Describes a multi-channel GPR configuration where there is more than one polarization of the antenna elements. The terminology will take on two forms namely, one when single lines are being surveyed in which case the PR-BD, PL-BD, PR-EF, PL-EF, X-POL terms are used whereas if an area is being covered we will have the XX, XY, YX, YY terminology being used. Refer to the pulseEKKO manual for more details. | ||
| nanosecond | ns | ns | 10-9s (One Billionth of a second) |
| odometer calibration value | ticks/m | Odometers and distance measuring indicators (DMI) are based on encoders that generate a defined number of electrical signals (normally referred to as ticks) per revolution of the encoder. When attached to a wheel, the wheel diameter dictates the distance travelled per revolution. To calculate an accurate measure of distance travelled, an “odometer calibration” is required which is usually attained by measuring the number of ticks that are observed when the wheel traverses a known distance. Calibration is the result of this measurement process converted to a value for the number of measured ticks per unit distance such as ticks/m. | |
| penetration depth | The maximum depth for buried targets for which reflected signals can be detected. When a GPR pulse travels into the ground, it decreases in amplitude because of geometrical spreading of the energy and absorption of the energy by the medium. At some point the signal amplitude gets so small that it is no longer detectable. The depth that the signal amplitude falls below detectability defines the penetration depth or depth of exploration. | ||
| picosecond | ps | A picosecond is 10−12 seconds (one trillionth of a second). | |
| point stacking | Term used to describe stacking (averaging of repetitive observations) at a single time point. Often done when using a Digital Equivalent Time Sampling (DETS) receiver. Stacking is carried out sequentially for all the points in a GPR trace. | ||
| Points per Trace (N): | N | the number of sample points in a GPR trace. | |
| Power Cable Detector | PCD | A sensor that detects the alternating current in electrical cables using the magnetic field intensity produced. The sensor is normally attuned to detect the magnetic fields that oscillate at 50 or 60 Hz which are the standard oscillation rate for power lines carrying electric current. | |
| pulse repetition frequency | PRF | kHz, MHz | acronym for pulse repetition frequency. For a GPR system, it is the number of times the transmitter emits a pulse in a second. |
| pulse repetition period | PRP | ms, us | acronym for the pulse repetition period. For a GPR system, this is the time interval between transmitter firings and is equal to 1/PRF. |
| pulser voltage: | volts | the peak amplitude of the voltage pulse applied to a GPR transmitting antenna. Impulsive GPRs are characterized by this voltage. This is a simple alternative means of defining the energy available to be emitted. Energy is stored in a source power supply and released when the transmitter is triggered. The GPR signal at a distance is directly proportional to the peak voltage. | |
| radio wave | Electromagnetic fields that travel through a material as waves. Radio signals which are commonly in the frequency range of 1 MHz to 1,000 MHz and electromagnetic waves in this frequency range are generally referred to as radio waves. (Electromagnetic signals in the 10, 000 MHz range are similarly referred to as microwaves. Light waves are just higher frequency electromagnetic waves.) | ||
| range resolution length | The minimum radial distance separation between two objects required so a GPR clearly detects two vertical responses. | ||
| receiver | Rx | General term for electronics device used to detect electromagnetic field strength and translate the signals into electrical voltages or currents to be recorded or displayed. Modern receivers generally convert the signals into digital values (numbers) for recording and display. | |
| reflection coefficient | normally named “Fresnel reflection coefficient”. Quantifies GPR signal reflection amplitude from a flat interface between two materials. | ||
| reflectivity | measure of signal amplitude returned by a target. | ||
| relative permittivity | K | See dielectric permittivity. | |
| resolution | The minimum separation of two objects before their individual responses merge into a single response. | ||
| ringing | Impulsive GPR signals can give rise to reverberating responses that oscillate for a much longer time than the GPR pulse or wavelet. Such a response is referred to as a “ringing” response or “ringing” for short. | ||
| sample point | Signal amplitude measured at specific point in time. | ||
| sample time interval | the time between success sample points on a trace which is usually a constant fixed value and is selected to assure that the Nyquist sampling criteria are met. | ||
| signal amplitude | The value assigned to amplitude of the radio wave signal at a point in time. | ||
| Signal-to-noise ratio | The ratio of GPR signal amplitude to the average noise amplitude. A large ratio results in a larger penetration depth or the ability to detect weaker signals. | ||
| Slice | Describes the GPR data in a time or depth slice when the data is displayed as a computer-generated image. | ||
| Spatial Filter | Spatial filters act on GPR data in the spatial (or positional) direction. These filters use adjacent traces during the filtering procedure and alter the shape of the trace through various mathematical manipulations designed to enhance or eliminate certain responses. For example, Background Subtraction is a spatial filter that removes flat-lying responses in the GPR data. | ||
| Spreading & Exponential Compensation Gain | SEC | SEC gain is a composite of a linear time gain and an exponential time gain which attempts to compensate for the spherical spreading losses and the exponential ohmic dissipation of energy with depth in the GPR Line. | |
| stacking | term used to describe recording many repetitions of a signal and computing the average value. | ||
| stacks | The number of repeated measurements averaged to get a resulting measurement. | ||
| station interval | Spatial distance between observation points along a survey traverse line or mesh points on a grid. | ||
| step size | See station interval. | ||
| system performance | Q | Measure of system exploration depth indicated by the ratio of transmitter output power or voltage to receiver noise power or voltage. | |
| time gain | GPR signal amplitudes decrease rapidly in amplitude versus delay time after the transmit pulse is emitted. Time gain is the term applied to the operation of applying an amplification, which increases with time, to the signal, attempting to compensate for large differences in signal amplitude. This is a non-linear operation. See gain. | ||
| time sampling interval | delta-t or Δt) | ns or ps | The time interval between sample points on GPR trace; usually a constant interval. The interval is usually adjusted to match the GPR frequency of operation and often set automatically by the system based on GPR frequency. |
| Time Slice: | is the term to describe the data acquired between two times – top of time slice and bottom of time slice. Most often a grid survey has the maximum time subdivided into a number of time slices of equal thicknesses. | ||
| Time Window | ns | The maximum recording time selected for a GPR measurement. Normally set in the field during measurement but can be reduced when viewing processing data after acquisition. | |
| Topography Files | A topography file is a text file containing GPR line positions and the elevations at those positions. When a topography file is attached to a GPR line, elevations for every GPR position are interpolated saved into the elevation field of the GPR trace header. | ||
| trace | Sequence of sample points from a single GPR channel that indicate the time variation of signal amplitude. | ||
| Trace Plot | Process of plotting traces side-by-side to create an apparent cross section of the ground. Trace number, which is normally equivalent to horizontal position, increases in the horizontal direction while data points on the trace are plotted in the vertical direction representing increasing signal delay time or depth. | ||
| Trace Repetition Rate | traces/second | the number of GPR traces that can be collected in a given time interval normally determined as 1/ (PRP x Points per trace x stacks) + delay time)). | |
| Trace Stacking | term used to describe stacking (recording and averaging) of complete traces. | ||
| Trace Time Interval: | Time between acquisition of sequential traces in free run data acquisition mode. | ||
| transducer | Name used where GPR antenna, electronics, and shield are combined into one physical unit. | ||
| transmitter | Tx | General term used for electronics devices used to create propagating electromagnetic fields | |
| Transmitter Output Voltage: | Volts (V) | the peak output amplitude of the transmitter electronics that is fed to the antenna. | |
| Two-dimensional (2D) array: | GPR array elements can be distributed over a flat surface to form a two-dimensional array of elements. (Note in some rare cases arrays may also be 3D) | ||
| Universal Transverse Mercator (UTM) | UTM | UTM is a geographic coordinate system that uses a 2-dimensional Cartesian coordinate system to give locations on the surface of the Earth. It is a horizontal position representation, i.e. it is used to identify locations on the Earth independently of vertical position but differs from the traditional method of latitude and longitude in several respects. | |
| UTM Letter | Each UTM zone is segmented into 20 latitude bands. Each latitude band is 8 degrees high and is lettered starting from “C” at 80°S, increasing up the English alphabet until “X”, omitting the letters “I” and “O” (because of their similarity to the numerals one and zero). The last latitude band, “X”, is extended an extra 4 degrees, so it ends at 84°N latitude, thus covering the northernmost land on Earth. Latitude bands “A” and “B” do exist, as do bands “Y” and “Z”. They cover the western and eastern sides of the Antarctic and Arctic regions respectively. | ||
| UTM Zone | The UTM system divides the Earth between 80°S and 84°N latitude into 60 zones, each 6° of longitude in width. | ||
| UTM Zone Number | Zone 1 covers longitude 180° to 174° W; zone numbering increases eastward to zone 60 that covers longitude 174 to 180 East. | ||
| velocity | v | m/ns or m/us | is the term used to characterize the speed at which GPR signals travel in a media. Velocity is a critical parameter when creating depth slice images and estimating depths of targets since velocity is used to convert travel-time to depth. |
| Vertical Filter | Applies a running average filter vertically (down-the-trace) to a GPR trace plot. The signal is averaged by replacing the data value at a given point by the average data value over a window centered about that point. Its primary purpose is to reduce random or high frequency noise by acting as a low pass temporal filter. | ||
| wavelet or EM pulse | Impulsive GPRs emit an oscillatory electromagnetic pulse which is short in time and space and is often referred to as a wavelet. | ||
| X Line Spacing: | the term used to refer to the spacing between X lines when a grid is covered by equispaced X lines. | ||
| X Line: | A line oriented in the X direction. (i.e. Y = constant while X position varies). This is a GPRLine convention when collecting GPR data in a grid. | ||
| X Slice: | time or depth slice image created from X lines in a grid. | ||
| XY Axes: | X and Y are the names given to the two orthogonal directions of a grid. When positioned at the specific corner of the grid which is selected to be the origin of the coordinate system and facing diagonally across the grid, the positive X direction runs to the right along the edge of the grid and the positive Y direction runs straight ahead. | ||
| XY Slice: | time or depth slice image created from combining both X and Y lines in a grid. | ||
| Y Line Spacing: | the term used to refer to the spacing between Y lines when a grid is covered by equispaced Y lines. | ||
| Y Line: | A line oriented in the Y direction. (i.e. X = constant while Y position varies). This is a GPRLine convention when collecting GPR data in a grid. | ||
| Y Slice: | time or depth slice image created from Y lines in a grid. | ||
| zero time | The time of first emission of signal by the transmitter. This time should be equated to the first break time unless the transmitter receiver separation is zero. | ||
| zone of influence | The size of an area on a reflecting feature that can be uniquely resolved. (See Fresnel zone definition and lateral resolution length). |