One of the major features of an observed space plume is the line-of-sight azimuth to the apparition, as it changes over the period of the observation. Together with an accurate knowledge of the observer's location, this can provide a vector pointing towards the object. When combined with a similar reading from another site some distance away [hundreds of kilometers, or more] this can provide an approximate location of the point which the object is over. Knowing the distance, and adding in another factor, the observed elevation angle, the actual altitude of the object above Earth's surface can be approximated.
|I'm using a handheld compass to get azimuth on Russian launch pad [and will determine distance by measuring time it takes for initial burst of engine noise to reach observation point], to verify which of several pads on Google-Earth image was used.|
There's only one catch with high-in-the sky rocket plumes. Among the hundreds of detailed observations I've studied, NOBODY had access to a magnetic compass or thought to use any other navigation functions of a handheld device [or to go back the next day WITH a compass to take sightings on horizon landmarks]. So the challenge is to derive the viewing azimuth solely from what's in the recorded images.
There are at least four methods to do this. First, if the sky is dark enough, stars may be visible, or the moon, and on-line programs can provide precise sky positions if the time/location of the event is known. Second, in the case of dashcam videos, the precise street may be identifiable [or the witness will provide it when queried], and using Google street-view will often locate the exact point along the street that the images were made -- the street azimuth can be provided by the application and the angle off from dead ahead can be estimated from the images. Third, a recognizable structure may allow orientation to be determined [examples: Tien An Min Square, or the Kiev seaport train terminal building, or Disneyland pavilions], which with on-line maps can be converted to azimuths. Fourth, in daytime, shadows of poles, building, or tall trees can be interpreted to indicate sun angle, that can be converted to azimuth with on-line astronomy applications [this method was used with the Chelyabinsk bolide, but I've never found it useful with rocket plumes which rarely even can be seen in full daylight].
Here are some starfield examples:
Even when stars are not visible, often the Moon is in the FOV:
Video of KYSS missile plume includes moon in FOV
When nothing is recognizable on the celestial sphere, the next most useful reference method is to identify the road the image [or dashcam video] was taken on. This can be labor-intensive [or require queries to the video poster], but again, in a surprisingly large number of cases, it works.
Finally, if you are lucky enough to get imagery with recognizable structures [especially with a sufficient distance between structures], the location of the observer can be estimated with adequate precision so that utilization of Google-Earth and 'street view' will work fine.
On rare occasions an image with a structure at known distance with estimatable height [how many floors, for example] can also be used as a measuring stick.
Also rare [but priceless when they DO become available] are videos from a street where overhead trolley lines provide a solid reference frame for even subtle motions of the plume, eliminating the effects of the maddingly frustrating tendency of imagers to pan/zoom and just bounce their camera aiming.
There is an entirely different approach to measuring distance to an on-orbit rocket plume, using an entirely different physical principle. The rocket itself draws an absolute-size measuring stick in the sky, that can be read.