JBO object to Shear Brook application

Professor Garrington has objected to the application on Shear Brook:

The amount of interference received at the telescope from a given location depends on the distance from the telescope and the intervening terrain as well as the strength of the emission itself. JBO has constructed detailed maps of the loss due to distance and terrain based on digital elevation data supplied by the Ordnance Survey and internationally recognised propagation models (ITU P.452). The calculations take into account diffraction over the terrain profile from each location to the focus of the Lovell Telescope and assume a frequency of 1.4 GHz, one of the key protected bands for radio astronomy and the typical observing frequency for the Lovell Telescope.

This analysis confirms that the proposed development itself is likely to generate interference which exceeds the internationally agreed threshold for what constitutes ‘detrimental interference’ to radio astronomy observations. This threshold is defined by the International Telecommunications Union in ITU-R 769 and is used in national and international spectrum policy negotiations.

This work has now been extended in order to put the potential emission from a proposed development in context of existing developments across a wide area (up to 40km from JBO). Again using high-resolution digital mapping from the Ordnance Survey the distribution of buildings can be overlaid on the radio loss map. In order to assess the relative contribution from different locations, the number of buildings and their area can be used as an indicator of the potential for radio interference. Hence estimates can be made for the potential interference arising from all development as a function of distance and direction from the telescope.

According to this analysis the proposed development could increase the total potential interference in that sector (10 degrees wide, out to 40km) by at least 10%. This is a significant contribution even as a single development and JBO would therefore oppose this development.”  Extract [our bold].

read the whole letter….

Jodrell Bank Observatory opposes this development and provides the following technical input

The University of Manchester’s Jodrell Bank Observatory (JBO) operates the 76-m Lovell Telescope along with other radio telescopes on the JBO site and across the UK as part of the e-MERLIN network. These radio telescopes, and the national and global networks which they are part of carry out unique and world-leading science across a wide range of astrophysics and cosmology. Facilities at JBO, including e-MERLIN, are used by most university astrophysics groups in the UK and by hundreds of scientists in the UK, Europe and across the globe.

Radio interference has an impact on almost all the observations which are carried out.  It may reduce the effective sensitivity of observations and the precision with which particular measurements can be made such as the precise timing of pulsars.

Searching for new pulsars is one example of scientific experiments which are now no longer feasible at Jodrell Bank, due to increased radio interference. In many observations it is the main factor which limits the quality of the data.

Much effort is already devoted to recognising and trying to remove the worst interference from observations, including the development of automated algorithms and careful scrutiny by expert observers. Every increase in the amount of interference makes this more difficult and may reduce the amount of useful data. Stronger signals can often be removed but this usually involves some degree of prejudice to separate terrestrial and astronomical signatures.

Interference is correlated with human activity, whether due to intentional transmissions or unintentional leakage from a wide range of electrical and electronic devices.

The amount of interference received at the telescope from a given location depends on the distance from the telescope and the intervening terrain as well as the strength of the emission itself. JBO has constructed detailed maps of the loss due to distance and terrain based on digital elevation data supplied by the Ordnance Survey and internationally  ecognised propagation models (ITU P.452). The calculations take into account diffraction over the terrain profile from each location to the focus of the Lovell Telescope and assume a frequency of 1.4 GHz, one of the key protected bands for radio astronomy and the typical observing frequency for the Lovell Telescope.

This analysis confirms that the proposed development itself is likely to generate interference which exceeds the nternationally agreed threshold for what constitutes ‘detrimental interference’ to radio astronomy observations. This threshold is defined by the International Telecommunications Union in ITU-R 769 and is used in national and  nternational spectrum policy negotiations.

This work has now been extended in order to put the potential emission from a proposed development in context of existing developments across a wide area (up to 40km from JBO). Again using high-resolution digital mapping from the Ordnance Survey the distribution of buildings can be overlaid on the radio loss map. In order to assess the relative contribution from different locations, the number of buildings and their area can be used as an indicator of the potential for radio interference. Hence estimates can be made for the potential interference arising from all development as a function of distance and direction from the telescope.

According to this analysis the proposed development could increase the total potential interference in that sector (10 degrees wide, out to 40km) by at least 10%. This is a significant contribution even as a single development and JBO would therefore oppose this development.

This development is by some margin the largest that has been proposed at this distance from the Observatory for many years. Its location has a direct line of sight to the telescope and hence there is no benefit of terrain shielding to the telescope.  It lies to the SW of the telescope where observations of pulsars (the main observing programme for the Lovell telescope at present) are often made with the telescope pointing at low elevation (close to the horizon).  Taking all these factors into account it poses a significant risk to the efficient operation of the Jodrell Bank telescopes as formulated in Policy PS10 of the Local Plan.

Simon Garrington

Jodrell Bank Observatory

University of Manchester

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