Condign volumes 1 to 3

Read from the scan by GLM-OCR; expect the odd misread word.

# UNCLASSIFIED SECRET UK RESTRICTED

around each charged particle in such a way as to compensate its charge.

14. In a two-component plasma with equal electron and ion temperatures it can be shown that the charge of the dynamic cloud of a single charged ion is composed of 50% attracted electrons and 50% of repelled ions. The roles of electrons and ions is reversed for the case of a negative ion. Hence, the number of electrons in the neutralising cloud may be small or large, depending on the densities and temperatures of the plasma components. Under these conditions a (EM) wave illuminating the plasma will set in motion the electrons in the clouds and if the scale of the dynamic cloud (Debye length) is much smaller than the wavelength of the illuminating wave, either coherent or collective scattering (from the electron component of the cloud) will occur.

15. It is beyond the scope of this brief paper to pursue the detail of the scattering other than to note that for radar-wave scattering to be enhanced there must be no interaction between the dust particles.

16. The intensity of the scattering, as a function of the incident radiation $ \lambda_{\mathrm{o}} $ equals $ 2\pi / k_{0} $ where $ k_{0} $ is the wave vector number. There are two regimes with little intensity for long wavelengths $ (2 k_{0} \lambda_{D}^{2} \leq 1) $ and a regime at shorter wavelengths $ (2 k_{0} \lambda_{D}^{2} \geq 1) $ . The radar scattering is caused by fluctuations of electron density. The scattered power per unit volume of illuminated plasma within an interval of solid angle, within a frequency interval $ d\omega $ and at wave vector k can be calculated from the Thomson electron cross section;

$$
\sigma_ {\mathrm {T}} = r _ {\mathrm {e}} ^ {2} = 7. 9 5 \times 1 0 ^ {- 3 0} \mathrm {m} ^ {2};
$$

where $ \mathrm{r_{e}}=2. 8 2 \times1 0^{-1 5} \mathrm{m} $ is the classical electron radius, $ \mathrm{E_{o}} $ is the incident (E field) amplitude and $ \varphi(\Omega) $ is a polarisation factor defined as:

$$
\varphi (\Omega) = \left| \frac {k _ {s} \left(k _ {s} E _ {s}\right)}{k _ {s} ^ {2} E _ {s}} \right| ^ {2}
$$

For backscatter $ \varphi(\Omega) $ equates to 1. The full derivation is $ \mathrm{at}^{[1]} $ .

17. Anomalous radar scatter has been received at RFs of 50,224 and 933MHz, using experimental radars. The plasma is not fully ionised.

18. Strong backscatter from this cause occurs principally at high latitudes, in the summer and at considerable altitude (~80km).

## DETECTION BY UK BASED RADARS

19. Backscatter from dusty' plasma at an altitude of, say, 80km could theoretically be obtained at a slant range of ~190km from a radar with a maximum elevation angle of $ \sim 2 5^{\circ} $ Those radars with a height-finding capability would soon reject the returns because the range/angle/altitude combination would place the target at an impossible altitude for manned

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20. The detection of phenomena other than mesosphere plasmas is also considered at Volume 3 and is necessarily classified SECRET as it involves the current detection performance of military operational systems.

## RADAR SIGHTING REPORTS

21. In an attempt to correlate simultaneous or sequential radar sightings with radar types, only limited UK information is available. In December 1989 5 NATO radars, part of ACCS, were within coverage range of a UAP report. Three radars had detections but two did not. Unfortunately, the radars have since been replaced and records of their parameters,