by neufer » Wed Dec 22, 2021 4:03 am
Chris Peterson wrote: ↑Tue Dec 21, 2021 5:18 pm
neufer wrote: ↑Tue Dec 21, 2021 4:59 pm
Chris Peterson wrote: ↑Tue Dec 21, 2021 3:51 pm
Interestingly, the comet's orbit intersects the orbit of Venus, so it may have created a new meteor shower on that planet.
Unfortunately, Venusians can't experience meteor showers (or even acid rain showers, for that matter).>>
99.9999% of the observed meteors on Earth are recorded with radar or by looking at radio signatures. So we just require Venusians with sufficient technology, or with senses in an unusual part of the EM spectrum.
https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Upper_atmosphere_and_ionosphere wrote:
<<Venus has an extended ionosphere located at altitudes 120–300 km. The ionosphere almost coincides with the thermosphere. The high levels of the ionization are maintained only over the dayside of the planet. Over the nightside the concentration of the electrons is almost zero. The ionosphere of Venus consists of three layers: v1 between 120 and 130 km, v2 between 140 and 160 km and v3 between 200 and 250 km. The maximum electron volume density (number of electrons in a unit of volume) of
3×105 cm−3 [electron plasma critical frequency ~5 MHZ] is reached in the v2 layer near the subsolar point. The upper boundary of the ionosphere (the ionopause) is located at altitudes 220–375 km and separates the plasma of the planetary origin from that of the induced magnetosphere. The main ionic species in the v1 and v2 layers is O
2+ ion, whereas the v3 layer consists of O
+ ions. The ionospheric plasma is observed to be in motion; solar photoionization on the dayside and ion recombination on the nightside are the processes mainly responsible for accelerating the plasma to the observed velocities. The plasma flow appears to be sufficient to maintain the nightside ionosphere at or near the observed median level of ion densities.>>
https://en.wikipedia.org/wiki/Ionosphere wrote:
<<The ionosphere is the ionized part of Earth's upper atmosphere, from about 48 km to 965 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F1 layer. The F2 layer persists by day and night and is the main region responsible for the refraction and reflection of radio waves.
As early as 1839, the German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field. Sixty years later, Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland using a 500 ft kite-supported antenna for reception. The transmitting station in Poldhu, Cornwall, used a spark-gap transmitter to produce a signal with a frequency of approximately
500 kHz [requiring ionospheric electron plasma densities > ~3,000 cm−3] and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Marconi achieved transatlantic wireless communications in Glace Bay, Nova Scotia, one year later.
In 1902, Oliver Heaviside proposed the existence of the Kennelly–Heaviside layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black-body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932 (and the development of high-frequency radio transceivers). Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties:
The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence. If the transmitted frequency is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal. It is calculated as shown below:
- Electron plasma critical frequency = sqrt{N} x 9kHZ (where N = electron density per cm3).
Objects in the Solar System that have appreciable atmospheres (i.e., all of the major planets and many of the larger natural satellites) generally produce ionospheres. Planets known to have ionospheres include Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The atmosphere of Titan includes an ionosphere that ranges from about 880 km to 1,300 km in altitude and contains carbon compounds. Ionospheres have also been observed at Io, Europa, Ganymede, and Triton.>>
https://en.wikipedia.org/wiki/Meteor_burst_communications wrote:
<<The earliest direct observation of interaction between meteors and radio propagation was reported in 1929 by Hantaro Nagaoka of Japan. In 1931, Greenleaf Pickard noticed that bursts of long-distance propagation occurred at times of major meteor showers. At the same time, Bell Labs researcher A. M. Skellett was studying ways to improve night-time radio propagation, and suggested that the oddities that many researchers were seeing were due to meteors. The next year Schafer and Goodall noted that the atmosphere was disturbed during that year's Leonid meteor shower, prompting Skellett to postulate that the mechanism was reflection or scattering from electrons in meteor trails. In 1944, while researching a radar system that was "pointed up" to detect the V-2 missiles falling on London, James Stanley Hey confirmed that the meteor trails were in fact reflecting radio signals. In 1946 the US Federal Communications Commission (FCC) found a direct correlation between enhancements in VHF (30 to 300 MHz) radio signals and individual meteors.
The first serious effort to utilize this technique was carried out by the Canadian Defence Research Board in the early 1950s. Their project, "JANET" (named for Janus, who looked both ways), sent bursts of data pre-recorded on magnetic tape from their radar research station in Prince Albert, Saskatchewan to Toronto, a distance exceeding 2,000 km. A 90 MHz "carrier" signal was monitored for sudden increases in signal strength, signalling a meteor, which triggered a burst of data. The system was used operationally starting in 1952, and provided useful communications until the radar project was shut down around 1960
As the Earth moves along its orbital path, millions of particles known as meteoroids enter the Earth's atmosphere every day, a small fraction of which have properties useful for point-to-point communication. When these meteoroids begin to burn up, they create a glowing trail of ionized particles (called a meteor) in the E layer of the atmosphere that can persist for up to several seconds. The ionization trails can be very dense and thus used to reflect VHF (30 to 300 MHz) radio waves. The frequencies that can be reflected by any particular ion trail are determined by the intensity of the ionization created by the meteor, often a function of the initial size of the particle, and are generally between
30 MHz and 50 MHz [electron densities: 11x106 to 31x106 cm−3].
The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the Earth where the meteoroid is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails only exist for fractions of a second to as long as a few seconds, they create only brief windows of opportunity for communications.>>
https://aquarid.physics.uwo.ca/research/radar/radarobserv.html wrote:
- The Department of Physics and Astronomy: Meteor Physics
<<Radio waves can reflect off ionized trails left behind as meteoroids ablate in the atmosphere. As the meteoroid moves through the atmosphere collisions with air molecules produce ions and electrons along the trail. The electrons are small enough to respond to the incident radio waves by vibrating themselves as dipole radiators. Provided the trail is small compared to the radio wave, the electrons will tend to reflect back to the radar in phase and produce a strong specular signal. This specular reflection implies that only that portion of the trail at right angles to the local apparent meteor radiant will contribute to the returned signal.
This specular scattering condition implies that meteors coming from a particular direction (a single radiant) will only be detected by the radar if they occur in a plane that has the radiant direction as the normal to the plane. When this echo plane constraint is combined with the ablation height of typical meteors (80 - 110 km), their intersection of the two produces an echo surface, where all radar meteor echoes from one radiant must occur as seen from the main radar site.
As seen from the main radar site, all meteors from a single meteor shower (having one radiant) will lie on this great circle. An example, shown below, for the Geminids, shows all echos from the shower detected over a one hour interval as a function of echo arrival azimuth and zenith distance. Here black dots show measured echo locations and open circles are theoretical echo line based on assumed radiant location and single height of ablation. Details of how this specular condition can be used to compute effective radar collecting areas can be found here.
The Western meteor physics group operates a triple-frequency, meteor orbital radar 100 km from London (near Tavistock, Ontario) where we record ~2500 meteoroid orbits per day. CMOR is a multi-frequency HF/ VHF radar used to detect the ionized trails associated with ablating meteoroids. It has been in single-station operation (echoes) since 1999 and multi-station (orbits) since January of 2002. The radar produces data on the range, angle of arrival, and velocity/orbit in some instances. To the end of 2009 we have measured 4 million individual orbits.>>
[quote="Chris Peterson" post_id=319187 time=1640107104 user_id=117706]
[quote=neufer post_id=319185 time=1640105960 user_id=124483]
[quote="Chris Peterson" post_id=319182 time=1640101863 user_id=117706]
Interestingly, the comet's orbit intersects the orbit of Venus, so it may have created a new meteor shower on that planet.[/quote]
Unfortunately, Venusians can't experience meteor showers (or even acid rain showers, for that matter).>>[/quote]
99.9999% of the observed meteors on Earth are recorded with radar or by looking at radio signatures. So we just require Venusians with sufficient technology, or with senses in an unusual part of the EM spectrum.[/quote][quote=https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Upper_atmosphere_and_ionosphere]
<<Venus has an extended ionosphere located at altitudes 120–300 km. The ionosphere almost coincides with the thermosphere. The high levels of the ionization are maintained only over the dayside of the planet. Over the nightside the concentration of the electrons is almost zero. The ionosphere of Venus consists of three layers: v1 between 120 and 130 km, v2 between 140 and 160 km and v3 between 200 and 250 km. The maximum electron volume density (number of electrons in a unit of volume) of [b]3×10[sup]5[/sup] cm[sup]−3[/sup] [color=#0000FF][electron plasma critical frequency ~5 MHZ][/color][/b] is reached in the v2 layer near the subsolar point. The upper boundary of the ionosphere (the ionopause) is located at altitudes 220–375 km and separates the plasma of the planetary origin from that of the induced magnetosphere. The main ionic species in the v1 and v2 layers is O[sub]2[/sub][sup]+[/sup] ion, whereas the v3 layer consists of O[sup]+[/sup] ions. The ionospheric plasma is observed to be in motion; solar photoionization on the dayside and ion recombination on the nightside are the processes mainly responsible for accelerating the plasma to the observed velocities. The plasma flow appears to be sufficient to maintain the nightside ionosphere at or near the observed median level of ion densities.>>[/quote][quote=https://en.wikipedia.org/wiki/Ionosphere]
[float=left][img3=Up, up, up, up to the Heaviside Layer]https://upload.wikimedia.org/wikipedia/commons/1/18/Atmosphere_with_Ionosphere.svg[/img3][img3=The Heaviside layer is the E region]https://upload.wikimedia.org/wikipedia/commons/7/7e/Ionosphere_Layers_en.svg[/img3][/float]
<<The ionosphere is the ionized part of Earth's upper atmosphere, from about 48 km to 965 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F1 layer. The F2 layer persists by day and night and is the main region responsible for the refraction and reflection of radio waves.
As early as 1839, the German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field. Sixty years later, Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland using a 500 ft kite-supported antenna for reception. The transmitting station in Poldhu, Cornwall, used a spark-gap transmitter to produce a signal with a frequency of approximately [b]500 kHz [color=#0000FF][requiring ionospheric electron plasma densities > ~3,000 cm[sup]−3[/sup]][/color][/b] and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Marconi achieved transatlantic wireless communications in Glace Bay, Nova Scotia, one year later.
In 1902, Oliver Heaviside proposed the existence of the Kennelly–Heaviside layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black-body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932 (and the development of high-frequency radio transceivers). Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties:
The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence. If the transmitted frequency is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal. It is calculated as shown below:
[list][b][color=#0000FF]Electron plasma critical frequency = sqrt{N} x 9kHZ (where N = electron density per cm[sup]3[/sup]). [/color][/b][/list]
Objects in the Solar System that have appreciable atmospheres (i.e., all of the major planets and many of the larger natural satellites) generally produce ionospheres. Planets known to have ionospheres include Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The atmosphere of Titan includes an ionosphere that ranges from about 880 km to 1,300 km in altitude and contains carbon compounds. Ionospheres have also been observed at Io, Europa, Ganymede, and Triton.>> [/quote][quote=https://en.wikipedia.org/wiki/Meteor_burst_communications]
<<The earliest direct observation of interaction between meteors and radio propagation was reported in 1929 by Hantaro Nagaoka of Japan. In 1931, Greenleaf Pickard noticed that bursts of long-distance propagation occurred at times of major meteor showers. At the same time, Bell Labs researcher A. M. Skellett was studying ways to improve night-time radio propagation, and suggested that the oddities that many researchers were seeing were due to meteors. The next year Schafer and Goodall noted that the atmosphere was disturbed during that year's Leonid meteor shower, prompting Skellett to postulate that the mechanism was reflection or scattering from electrons in meteor trails. In 1944, while researching a radar system that was "pointed up" to detect the V-2 missiles falling on London, James Stanley Hey confirmed that the meteor trails were in fact reflecting radio signals. In 1946 the US Federal Communications Commission (FCC) found a direct correlation between enhancements in VHF (30 to 300 MHz) radio signals and individual meteors.
The first serious effort to utilize this technique was carried out by the Canadian Defence Research Board in the early 1950s. Their project, "JANET" (named for Janus, who looked both ways), sent bursts of data pre-recorded on magnetic tape from their radar research station in Prince Albert, Saskatchewan to Toronto, a distance exceeding 2,000 km. A 90 MHz "carrier" signal was monitored for sudden increases in signal strength, signalling a meteor, which triggered a burst of data. The system was used operationally starting in 1952, and provided useful communications until the radar project was shut down around 1960
As the Earth moves along its orbital path, millions of particles known as meteoroids enter the Earth's atmosphere every day, a small fraction of which have properties useful for point-to-point communication. When these meteoroids begin to burn up, they create a glowing trail of ionized particles (called a meteor) in the E layer of the atmosphere that can persist for up to several seconds. The ionization trails can be very dense and thus used to reflect VHF (30 to 300 MHz) radio waves. The frequencies that can be reflected by any particular ion trail are determined by the intensity of the ionization created by the meteor, often a function of the initial size of the particle, and are generally between [b]30 MHz and 50 MHz [color=#0000FF][electron densities: 11x10[sup]6[/sup] to 31x10[sup]6[/sup] cm[sup]−3[/sup]][/color][/b].
The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the Earth where the meteoroid is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails only exist for fractions of a second to as long as a few seconds, they create only brief windows of opportunity for communications.>>[/quote][quote=https://aquarid.physics.uwo.ca/research/radar/radarobserv.html]
[list][size=150]The Department of Physics and Astronomy: Meteor Physics[/size][/list]
<<Radio waves can reflect off ionized trails left behind as meteoroids ablate in the atmosphere. As the meteoroid moves through the atmosphere collisions with air molecules produce ions and electrons along the trail. The electrons are small enough to respond to the incident radio waves by vibrating themselves as dipole radiators. Provided the trail is small compared to the radio wave, the electrons will tend to reflect back to the radar in phase and produce a strong specular signal. This specular reflection implies that only that portion of the trail at right angles to the local apparent meteor radiant will contribute to the returned signal.
This specular scattering condition implies that meteors coming from a particular direction (a single radiant) will only be detected by the radar if they occur in a plane that has the radiant direction as the normal to the plane. When this echo plane constraint is combined with the ablation height of typical meteors (80 - 110 km), their intersection of the two produces an echo surface, where all radar meteor echoes from one radiant must occur as seen from the main radar site.
As seen from the main radar site, all meteors from a single meteor shower (having one radiant) will lie on this great circle. An example, shown below, for the Geminids, shows all echos from the shower detected over a one hour interval as a function of echo arrival azimuth and zenith distance. Here black dots show measured echo locations and open circles are theoretical echo line based on assumed radiant location and single height of ablation. Details of how this specular condition can be used to compute effective radar collecting areas can be found here.
The Western meteor physics group operates a triple-frequency, meteor orbital radar 100 km from London (near Tavistock, Ontario) where we record ~2500 meteoroid orbits per day. CMOR is a multi-frequency HF/ VHF radar used to detect the ionized trails associated with ablating meteoroids. It has been in single-station operation (echoes) since 1999 and multi-station (orbits) since January of 2002. The radar produces data on the range, angle of arrival, and velocity/orbit in some instances. To the end of 2009 we have measured 4 million individual orbits.>>[/quote]