Randy Zipser
EF3
Let me say at the outset that the purpose of this discussion is not to criticize or tell any storm chaser how to go about their business. Rather, my interest here is to offer some educational insights and practical tips to help make the products of their efforts more useful and valuable from a scientific standpoint.
Nowadays, more-and-more storm chasers are taking evermore risk in getting themselves closer-and-closer to tornado funnels to capture the most “insane” video humanly possible. Why should these chasers not also take the opportunity to capture video images that will maximize usefulness to meteorological research by correctly capturing lofted solid debris for post-analysis and scientific research? In return, their video contributions are helping to advance understanding of one of Nature’s most unusual phenomena…and what they experience are incredibly rare chances to get “up close-up-and-personal” to tornadoes and to learn their “secrets,” at least, that which has eluded human knowledge thus far.
As it turns out, the process, known as terrestrial photogrammetry, or photogrammetry, for short, employed to achieve the desired end result (tornado wind speed determination), is very well known and documented, and has been around since 1867. However, this “procedure” depends upon very accurate data to be input in order to obtain correct results. That’s where “extreme” storm-chasers come into the picture. Only storm chasers who seek close-up encounters with a tornado “debris cloud” near the ground can provide such very rare images for scientific post-analysis.
But you’re probably wondering, ”What, exactly, is photogrammetry, and what does it entail that is so important for determination of wind speeds in tornadoes?”
I’ll answer that question later, but first, a little background about photogrammetry, particularly, terrestrial photogrammetry.
Photogrammetry is derived from the words “photo” and “meter,” and it refers to measurements taken from images. It uses a camera to capture images on the ground, which can then be used to measure distances between points (landmarks) on the image using known scaled maps (e.g., USGS Topographic Maps) of the area. It entails a procedure for documenting, measuring, and analyzing terrestrial (i.e., ground-based) pictures. It is both a science and technology because it takes photographs and applies technology to obtain meaningful findings. Modern photogrammetry employs image types other than photographs, such as digital video.
Proper image retrieval, image processing, control data for image correction, data accumulation, and presentation of end-product outcomes comprise the photogrammetric process. Photographs or images for photogrammetry are taken with a specialized (metric) camera or a standard video camera (the preference of most storm chasers). Images are acquired and recorded traditionally using a tripod (terrestrial photogrammetry) set up and mounted on the ground.
Technically-speaking, terrestrial photogrammetry is a form of metric photogrammetry, which entails taking exact measurements on pictures or video imagery on the ground in order to identify relative locations of points. Growth of the high-tech industry and the proliferation of digital cameras has resulted in lighter, more precise equipment and streamlined procedures in the field. There has also been a significant decrease in cost which has allowed increased productivity over the past decade.
For the tornado researcher, photogrammetry can be used to solve scaling problems. In the simplest case, if the scale(s) of the picture or image is known, the distance between two points on a plane parallel to the photographic image plane can be estimated by measuring their distance on the image.
The primary benefits of photogrammetry are: the ease and speed (not to mention, fun!) with which data may be acquired; the acquired data is permanent and accurate, and it captures the condition at the moment the image(s) were taken in both pictorial or metric versions; and, because the information acquired is permanent, it is much easier to re-survey or re-evaluate the site to confirm or obtain any missing information (this is an essential step in the photogrammetry procedure).
During this re-survey step, a surveyor transit is used. A surveyor transit is an optical instrument often used by civil engineers in surveying to measure horizontal and vertical angles. It typically consists of a telescope mounted on a tripod, allowing for precise measurements in land assessments. This procedure is important for the accurate determination of tornado wind speeds because a tornado wind speed is really the equivalent of a mathematical vector between two points (locations) on the same image. That wind speed vector is also defined by a horizontal (tangential) and vertical (up-and-down) component (which could also signify updraft or downdraft velocity). But, in order for the tangential component to be really accurate, the true horizon on the image plane must first be determined. The surveyor transit assists in locating true horizon using permanent “landmarks” (e.g., treetops, water/microwave towers, tall buildings, grain silos, power poles, etc.) in the background of the image, which is then transferred to the image plane.
That’s basically how meteorologists and researchers turn “data” on tornado video images into tornado wind speeds.
However, to ensure that the tornado researcher has the proper “data” to input, the storm chaser must first provide imagery that allows the researcher to do the proper scaling and calculations (which, today, are done using computer software, unlike decades ago when manual tracking techniques and calculations were employed).
So, just what should a proper video image contain for post-research analysis? The following is a list of what the storm chaser’s “perfect video” should include for scientific research:
It is my hope that this information is useful and, ideally, finds it way into the memory banks of the very-best and most-successful storm chasers known on the Internet and to social-media platforms nowadays.
Nowadays, more-and-more storm chasers are taking evermore risk in getting themselves closer-and-closer to tornado funnels to capture the most “insane” video humanly possible. Why should these chasers not also take the opportunity to capture video images that will maximize usefulness to meteorological research by correctly capturing lofted solid debris for post-analysis and scientific research? In return, their video contributions are helping to advance understanding of one of Nature’s most unusual phenomena…and what they experience are incredibly rare chances to get “up close-up-and-personal” to tornadoes and to learn their “secrets,” at least, that which has eluded human knowledge thus far.
As it turns out, the process, known as terrestrial photogrammetry, or photogrammetry, for short, employed to achieve the desired end result (tornado wind speed determination), is very well known and documented, and has been around since 1867. However, this “procedure” depends upon very accurate data to be input in order to obtain correct results. That’s where “extreme” storm-chasers come into the picture. Only storm chasers who seek close-up encounters with a tornado “debris cloud” near the ground can provide such very rare images for scientific post-analysis.
But you’re probably wondering, ”What, exactly, is photogrammetry, and what does it entail that is so important for determination of wind speeds in tornadoes?”
I’ll answer that question later, but first, a little background about photogrammetry, particularly, terrestrial photogrammetry.
Photogrammetry is derived from the words “photo” and “meter,” and it refers to measurements taken from images. It uses a camera to capture images on the ground, which can then be used to measure distances between points (landmarks) on the image using known scaled maps (e.g., USGS Topographic Maps) of the area. It entails a procedure for documenting, measuring, and analyzing terrestrial (i.e., ground-based) pictures. It is both a science and technology because it takes photographs and applies technology to obtain meaningful findings. Modern photogrammetry employs image types other than photographs, such as digital video.
Proper image retrieval, image processing, control data for image correction, data accumulation, and presentation of end-product outcomes comprise the photogrammetric process. Photographs or images for photogrammetry are taken with a specialized (metric) camera or a standard video camera (the preference of most storm chasers). Images are acquired and recorded traditionally using a tripod (terrestrial photogrammetry) set up and mounted on the ground.
Technically-speaking, terrestrial photogrammetry is a form of metric photogrammetry, which entails taking exact measurements on pictures or video imagery on the ground in order to identify relative locations of points. Growth of the high-tech industry and the proliferation of digital cameras has resulted in lighter, more precise equipment and streamlined procedures in the field. There has also been a significant decrease in cost which has allowed increased productivity over the past decade.
For the tornado researcher, photogrammetry can be used to solve scaling problems. In the simplest case, if the scale(s) of the picture or image is known, the distance between two points on a plane parallel to the photographic image plane can be estimated by measuring their distance on the image.
The primary benefits of photogrammetry are: the ease and speed (not to mention, fun!) with which data may be acquired; the acquired data is permanent and accurate, and it captures the condition at the moment the image(s) were taken in both pictorial or metric versions; and, because the information acquired is permanent, it is much easier to re-survey or re-evaluate the site to confirm or obtain any missing information (this is an essential step in the photogrammetry procedure).
During this re-survey step, a surveyor transit is used. A surveyor transit is an optical instrument often used by civil engineers in surveying to measure horizontal and vertical angles. It typically consists of a telescope mounted on a tripod, allowing for precise measurements in land assessments. This procedure is important for the accurate determination of tornado wind speeds because a tornado wind speed is really the equivalent of a mathematical vector between two points (locations) on the same image. That wind speed vector is also defined by a horizontal (tangential) and vertical (up-and-down) component (which could also signify updraft or downdraft velocity). But, in order for the tangential component to be really accurate, the true horizon on the image plane must first be determined. The surveyor transit assists in locating true horizon using permanent “landmarks” (e.g., treetops, water/microwave towers, tall buildings, grain silos, power poles, etc.) in the background of the image, which is then transferred to the image plane.
That’s basically how meteorologists and researchers turn “data” on tornado video images into tornado wind speeds.
However, to ensure that the tornado researcher has the proper “data” to input, the storm chaser must first provide imagery that allows the researcher to do the proper scaling and calculations (which, today, are done using computer software, unlike decades ago when manual tracking techniques and calculations were employed).
So, just what should a proper video image contain for post-research analysis? The following is a list of what the storm chaser’s “perfect video” should include for scientific research:
- The storm chaser (observer) MUST remain in a fixed, stationary position relative to the moving funnel. This requirement is absolutely essential because both the observer and the tornado (forward translation) cannot be in motion at the same time in order to compute wind speed around the base of the funnel.
- The storm chaser should always try to seek a safe, unobstructed view where the bottom of the funnel (i.e., the damage “debris”) is always visible, for period of several continuous minutes, if possible, without moving.
- The storm chaser’s video camera should always be solidly-mounted to a ground-based tripod or, better yet, a swing-arm mounted to the exterior of the chase vehicle which allows the camera to remain steady during the entire time that the video is being taken (and having the ability for the lens to be easily wiped of water droplets from rain, if necessary).
- If the storm chaser can see a long stretch of open range land or agricultural crop fields in the estimated path of the funnel having no man-made structures or tree-breaks in its immediate path, this would be a good time to visually document the tornado funnel column and/or the rotating cloud-base at the very top of the funnel. Such imagery also may assist in research about the funnel’s overall structure and perhaps even wind speeds could obtained from discrete cloud-tag features rotating around the top of the funnel. (Cloud-tags often form and dissipate rapidly, so are not generally reliable indicators for rotational wind speed motion at/near cloud-base level.)
- The storm chaser should move forward only after the tornado funnel traverses the entire visible image at the current stationary position to keep up with the funnel and seek the next stationary position for the next sequence of video, then repeat the process described in step (1) above.
- The storm chaser should always set the zoom setting on the video camera to show clearly the entire width of the visible debris cloud, even if this is larger than the width of the visible condensation funnel, and (VERY IMPORTANT!) leave the zoom setting alone until ready to change observer position [see step (5)]. There is nothing more annoying than seeing zooming in-and-out on the debris cloud [which also makes following (tracking) of a given debris element much more difficult, if not impossible]!
- If there are no background permanent landmarks visible in the background field of view, the storm chaser should try to stop where some unique item (e.g., a fence-post sign, tin-horn, power-pole number or tag, etc.) is visible in foreground, in order to relocate the position later during the post-survey. Written or verbally-recorded notes describing exact position (including vehicle odometer reading from some previously-recorded intersection with a main highway, for example) might also come in handy later, particularly if the chaser is on an unpaved section road away from a main highway.
- If possible, the storm-chaser should open the windows (provided there is no precipitation overhead, hail falling, or blowing dust), and idle the engine, to capture the sound of wind (or any other unusual sound, such as a “roar”) that may emanate from the tornado (or inflow) as it approaches the chaser’s position. The less background chatter, the better, although that is always not possible in stressful situations.
It is my hope that this information is useful and, ideally, finds it way into the memory banks of the very-best and most-successful storm chasers known on the Internet and to social-media platforms nowadays.
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