Lead Scientist: Prof. Umran Inan, Dr. Morris Cohen and Dr Deborah Scherrer
Organization: Stanford University, US
AWESOME and SID are the name of the ELF/VLF receivers (radio signals between 300Hz and 50kHz)
- AWESOME – Atmospheric Weather Electromagnetic System for Observation, Modeling, and EducationThe AWESOME receiver detects a number of single-frequency radio station (there are roughly 20 in operation on Earth, look at footnote 1), but also a lot of broadband natural signals, such as those which are emitted by lightning and wave-particle interactions in the Earth’s magnetosphere.AWESOME
- monitors amplitude and phase of VLF transmitter signals, with 50 Hz time resolution.
- can save entire radio spectrum between 300
Hz and 50 kHz, to detect natural signals (sferics, whistlers, chorus, hiss)
- SID – Sudden Ionospheric DisturbanceThe SID monitor is a simpler version, intended for educational uses, that primarily records the single-frequency radio stations. SID monitors
- amplitude of VLF transmitter signals with 0.2 Hz time resolution
Monitoring the strength of these signals (single-frequency radio stations) serves as an ionospheric diagnostic, since the propagation of the radio signals from
transmitter to receiver relies on the conditions of the lower ionosphere.
Receivers AWESOME and SID are created at Stanford University for training purposes. Now AWESOME and SID are global programs. There are more than 30 AWESOMEs and 300 SIDs deployed all over the world. (see map below)
|AWESOME Program Home Page||SID Program Home Page
SID Data Browser
ELF and VLF studies in few words. (look at footnote 2)
- The set of sound files which are referred to in presentation above.
- chorus wave observed on satellite
- VLF ‘click’ sferics observed by an AWESOME receiver
- VLF hiss observed by an AWESOME receiver
- VLF ‘pop’ sferics observed by an AWESOME receiver
- VLF ‘tweek’ sferics observed by an AWESOME receiver
- VLF whistler observed by an AWESOME receiver
- All sound files at once (right click and Save Target as)
NOTE: To listen to audio, you must install the appropriate additions to your browser.
- Morris B. Cohen, Umran S. Inan and Evans W. Paschal. Sensitive Broadband ELF/VLF Radio Reception With the AWESOME Instrument, IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING (the AWESOME receiver )
- Deborah Scherrer, Morris Cohen, Todd Hoeksema, Umran Inan, Ray Mitchell, Philip Scherrer. Distributing space weather monitoring instruments and educational materials worldwide for IHY 2007: The AWESOME and SID project, Advances in Space Research 42 (2008) 1777-1785 (the global scientific outreach program)
|Table of VLF transmitters|
|59.91||10.52||16400Hz||JXN||Kolsas, Norway (NATO)||FSK||45|
|52.71||-3.07||19600Hz||GBZ||Anthorn, Great Britain (NATO)||FSK||30|
|-21.80||114.20||19800Hz||NWC||North West Cape, Australia (USA)||MSK||1000|
|40.88||9.68||20270Hz||ICV||Isola di Tavolara, Italy (NATO)||MSK||20|
|20.40||-158.2||21400Hz||NPM||Lualualei, Hawaii, USA||MSK||424|
|40.70||1.25||21750Hz||HWV||Le Blanc, France (NATO)||MSK||200|
|52.40||-1.20||22100Hz||GQD||Anthorn, Great Britain (NATO)||FSK|
|53.10||7.60||23400Hz||DHO||Rhauderfehn, Germany (DHO)||FSK||800|
|44.65||-67.30||24000Hz||NAA||Cutler, Maine, USA||MSK||1000|
|48.20||-121.9||24800Hz||NLK||Jim Creek, Washington, USA||MSK||192|
|46.35||-98.33||25200Hz||NLM||LaMoure, North Dakota, USA||MSK|
|65.00||-18.00||37500Hz||NRK||Grindavik, Iceland (USA)||MSK|
|18.00||-67.00||40750Hz||NAU||Aguado, Puerto Rico (USA)||MSK||100|
|38.00||13.50||45900Hz||NSC||Sicily, Italy (USA)||MSK|
Since ELF and VLF studies fall in the 300 Hz – 30 kHz, they line up well with the frequencies of audio recognition. Hence, we can listen to the data stream as if it were audio. Here’s a selected segment of data taken from Stanford, California. (To listen, click vlf_ns.) NOTE: To listen to audio, you must install the appropriate additions to your browser.
- In this file, listen for three distinct types of sounds.
- The first and most prevalent is a series of clicks and pops. These signals, called „radio atmospherics“ are short bursts of radiation originating from lightning strikes, which could be anywhere in the world. Most of the VLF/ELF energy released by lightning is trapped between the Earth and ionosphere, and thus can travel around the world.
- The second type signal you’ll hear is a falling pitch, lasting a couple seconds, known for this reason as a „whistler“. Whistlers are also comprised of energy released from lightning, except instead of propagating directly, these signals actually escape the atmosphere entirely, propagate along magnetic field lines and within the radiation belts (causing different frequencies to travel at different speeds), and land at the other end, where they reenter the atmosphere.
- The third and final noise is a VERY high pitched tone (you may have trouble hearing it, but it is there). You’ll notice a pattern to it – 1,2,3, pause,1,2,3, pause… These are the `Alpha’ navigation beacons operated in Russia, and are an example of a VLF transmitter, which can be used to remotely sense disturbances in the ionosphere.
Another way of presenting VLF data is in the form of a spectrogram, and here is an example of the same data in this form:
The data are divided up into small time segments, in this case 10 ms long. A Fourier transform is performed on each segment, and the color shows the magnitude of the signal.
The numerous vertical lines on these spectrograms are radio atmospherics, or `sferics’, originating from lightning strikes, which could be anywhere in the world. Lightning emits short bits of impulsive radiation which can observed be at global distances from the source since they are guided by the Earth-ionosphere waveguide. These correspond to the „click“ and „tweek“ sounds in the audio sample. A zoom-in a radio atmospheric is shown in the bottom left panel.
There are also a set of short horizontal lines between 10 and 15 kHz. These are the `Alpha’ navigation beacons.
The solid horizontal lines between 18 and 30 kHz are VLF transmitter signals, although they are too high in frequency to hear in the audio. These transmitter signals are nominally used for communications. The top right panel shows a zoom-in of a transmitter called NWC, in Australia, which is clearly detected at Stanford, and the communication signal can be seen as up and down modulation of the frequency. However, these transmitter signals act as a diagnostic of the lower ionosphere, since their propagation to long distances is dependent on ionospheric reflection. The bottom right panels shows an example of two of these VLF transmitters tracked at Stanford for a 3-day period. Both the amplitude (top) and phase (bot) of the signal show a clear daily variation, reflecting the drastic changes to the lower ionosphere from daytime to nightime. This is an example of ionospheric remote sensing using VLF transmitter signals.