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Mainland Experiments

Description of the currently available mainland (UHF and VHF) experiment modulation schemes.

The current set of mainland experiments contains modulation schemes of two kinds. The newer generation of mainland experiments (arc1, arc_dlayer, arc_dlayer_ht, dlayer, manda, pia, tau1, tau2, tau2_pl, tau3, tau7 and tau8) all exploit the much improved signal processing capabilities of the mainland radars. They mostly use alternating codes, allowing the possibility of much improved spatial resolution. In addition, the arc1 experiment uses “time slicing” in order to make spectral measurements at 0.44 seconds resolution, the best ever achieved by EISCAT.

The older generation of mainland experiments (cp1lt, cp4bv and cp7hv) are the so-called “retro fits”. These experiments are more or less identical to those run before the renovation of the mainland radars, which started in early 2000. These experiments are based on long pulses and short pulse “power profiles”, though the cp1lt modulation also includes an alternating code covering altitudes up to about 375 km.

The arc1, pia, tau2, tau2_pl, tau3 and cp1lt experiments are for the UHF radar. The tau1, tau7, tau8, cp4bv and cp7hv experiments are for the VHF radar. Versions of the arc_dlayer, arc_dlayer-ht, d-layer and manda experiments exist for both mainland radar systems.

New-generation mainland experiments

The documentation available for EISCAT experiments is still rather patchy in some instances. Where documentation is available on EISCAT's web pages, links are provided below. Further links will be added as time permits.

arc1 - The arc1 experiment is a high time-resolution code for the Tromso and remote UHF systems, which exploits time-slicing techniques to achieve a time resolution of 0.44s. See EISCAT's annotated experiments page and EISCAT's arc1 documentation. Arc1 data can be analysed by all the command-line versions of guisdap since g8.1.

arc_dlayer - The arc_dlayer experiment uses the same code set as for arc1, but includes the calculation of interpulse lags for the calculation of long d-layer autocorrelation functions. See the annotated experiments page. Arc_dlayer data can be analysed by all the command-line based versions of guisdap since g8.2.

arc_dlayer_ht - This is a high-time resolution version of arc_dlayer, for which no documentation is available as yet. The analysis of this experiment is not yet supported by GUISDAP.

d-layer - This is a specialised d-layer experiment, mainly intended for the VHF radar, covering the range interval from 60 to 126.6km, with a range increment of 600m. The standard version of this experiment uses the whole antenna, though versions also exist for split-beam operation and also for use on the UHF radar. See the annotated experiments page. Data from the d-layer experiment can be analysed by all of the command-line based versions of guisdap since g8.2.

manda - The manda experiment is a relatively new code, intended to combine D-region observations with some degree of F-region coverage, e.g. to monitor the corresponding electric field. No detailed documentation exists at present. Analysis of manda data is supported by the command-line based version of GUISDAP under versions g8.4 and g8.5 only

pia - This experiment was really designed as a fix to allow some kind of useful measurements at low duty cycle, to get around some transmitter problems which were experienced immediately after the renovation. It uses a 300 us pulse with a 3 bit binary code, giving an effective range resolution of 15 km. Sampling is done at 10 us, so although the apparent range resolution is 1.5 km, adjacent data are highly non-unique. Thirty samples are calculated for each range, at 10 us spacing. Range coverage is from 90 to 375 km, so this experiment is not useful for studying the topside ionosphere. There is no power profile measurement as such, though a “pseudo power profile” can be computed from the zero lag profile. Because it was really only intended as a solution to provide some measurements in the case of a limited duty cycle, pia has now effectively been superseded by other experiments, such as tau2_pl. Analysis of pia is supported under all the command-line based versions of guisdap, starting from g8.1.

Code Pulse Length Start Range End Range Range Res.
Long Pulse 100 us (x3) 90 390 15

tau1 - The tau1 code is intended to be a general purpose VHF experiment, aimed at experiments with cp4-like geometries, observing a long latitudinal slice through the F-region at low elevation. It is somewhat similar to the tau2 program decsribed below. For a more detailed description see the annotated experiments page or the tau1 documentation. Analysis of tau1 data is supported under all the command-line based versions of guisdap, starting from g8.1.

tau2 – This is intended to be a general purpose UHF experiment covering all altitudes from 90 to 750 km using only 16-bit alternating codes. The alternating code has a 36 us baud, with 12 us sampling. The sample resolution is therefore 1.8 km, but unique data are only available at 5.4 km range resolution. There is no ion line power profile measurement as such, though a “pseudo power profile” can be computed from the first lag profile. Analysis of tau2 data is supported under all the command-line based versions of guisdap, starting from g8.1.

Code Pulse Length Start Range End Range Range Res.
Power Profile 2us (x 13) 63 198 0.3
Power Profile 2 us (x 13) 63 198 0.3
Alt. Code 36 us (x 16) 90 720 5.4

tau2_pl - Later versions of the tau2 code, now in standard use for mainland Common Programmes, have two Barker coded power profiles added to the end of the dump, covering ranges 63 to 198 km at 0.3 km resolution, intended for the study of plasma lines. For a full description of the experiment files, see EISCAT's tau2_pl page. Analysis of tau2_pl data is supported by g8.2 and later versions of the command-line based form of guisdap.

tau3 – This experiment uses an identical modulation to tau2, but the number of signal samples is doubled by using a longer reception phase (twice as long as tau2) to allow the calculation of gates out to much longer range. The power profile data is in theory identical to tau2, but in practice the power profiles have never been used and the transmission of the Barker coded power profile pulse is probably turned off. The tau3 experiment is used for low elevation and scanning experiments where long range coverage is needed to get data from ionospheric altitudes. Remote site reception is the same as for tau2. Analysis of the Tromso data is possible using either GUISDAP1 or GUISDAP2. Analysis of the remote data should be possible using GUISDAP1. The same analysis problem with ranges around 190 km as encountered in tau2 analysis is also present in tau3. However, because tau3 is normally run with elevations far from vertical, this range is normally at quite low altitude and therefore does not significantly affect the analysis. Analysis of tau3 data is supported by all the command-line based forms of GUISDAP, starting from g8.1.

Code Pulse Length Start Range End Range Range Res.
Power Profile 2us (x 13) 63 198 0.3
Power Profile 2us (x 13) 63 198 0.3
Alt. Code 36us (x 16) 90 1400 5.4

tau7 - This is a VHF programme, intended as an optimised replacement for cp7, which focuses on observations from the ionospheric topside. In practice, the experiment has not been run very much. Analysis of tau7 data is supported by all versions of the command-line based form of guisdap, starting from g8.1.

tau8 - This is a VHF programme, similar to tau1, intended for use in low-elevation experiments. Although it was originally designed for dual-beam use, it has also been adopted in single-beam applications, including experiments carried out in support of Cluster. Analysis of tau8 data is supported by all versions of the command-line based form of guisdap, starting from g8.1.

Retro-Fit Experiments

As stated above, the first experiments to be implemented on the post-renovation mainland radars were basically copies of the old pre-renovation Common Programme modulations, which had been re-written to run on the new operating system. Although such experiments are not really used any more, they are included here for the benefit of users working with archive data from the period immediately after September 2000.

cp1l – This is essentially the old pre-renovation cp1k experiment, re-engineered to run on the new system, with the data stored as lag profiles. Documentation can be found on EISCAT's cp1lt page As with cp1k, the experiment uses a 16-bit alternating code of bit length 21 us, with 7us sampling. The sample resolution is therefore 1.05 km, but unique data are only available at 3.15 km range resolution. The long pulse part of the experiment uses a 350 us long pulse, and there are two power profiles calculated from pulses of length 21 us (for consistency with the alternating code) and 40 us. As with the alternating code, the 21 us power profile is sampled at 7 us resolution, giving an apparent range resolution of 1.05 km, but unique data are only available at 3.15 km resolution. The 40 us power profile is sampled at 10 us, so the apparent range resolution is 1.5 km, but unique data are only available every 6km. Integer lags to lag 16 are calculated from the alternating code, while thirty lags at 12 us spacing are calculated from the long pulse data. As with cp1k, the remote sites receive both the alternating code and long pulse. The remote analysis currently available at RAL uses only the long pulse data. Analysis of cp1l data is supported by all command-line based versions of guisdap, starting with g8.1.

Code Pulse Length Start Range End Range Range Res.
Power Profile 21 63 377 3.15 (1.05)
Power Profile 40 75 433 6 (1.5)
Alt. Code 21us (x16) 90 338 3.15 (1.05)
Long Pulse 350 us 160 720 52.5

cp4b - This experiment was the re-implementation of the pre-renovation cp4 experiment, intended for use on the VHF in northward-looking low-elevation applications, and now superseded by tau1. Analysis for the cp4b data is supported in versions g8.4 and g8.5 of the command-line based version of guisdap.

cp7h - This experiment was the re-implementation of the pre-renovation cp7 experiment, intended for use on the VHF in vertical-looking experiments to study the ionospheric topside, now superseded by tau7. Analysis of cp7h data is supported by all the command-line based versions of guisdap, starting from g8.1.