From 6689ec17417d11d7d48f83e4a7fdb89748a3d14e Mon Sep 17 00:00:00 2001 From: Ollie Ballinger <58981760+oballinger@users.noreply.github.com> Date: Fri, 11 Feb 2022 18:05:19 +0000 Subject: [PATCH] Update README.md --- README.md | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/README.md b/README.md index acf3514..ff6e454 100644 --- a/README.md +++ b/README.md @@ -19,17 +19,17 @@ Below is a screenshot of the tool in use with five labeled components, each of w # How it works -While most satellite imagery is optical, meaning it captures sunlight reflected by the earth’s surface, Synthetic Aperture Radar (SAR) satellites such as Sentinel-1 work by emitting pulses of C-band radio waves and measuring how much of the signal is reflected back. This is similar to the way a bat uses sonar to “see” in the dark: by emitting calls and listening to echoes. +While most satellite imagery is optical, meaning it captures sunlight reflected by the earth’s surface, Synthetic Aperture Radar (SAR) satellites such as Sentinel-1 work by emitting pulses of radio waves and measuring how much of the signal is reflected back. This is similar to the way a bat uses sonar to “see” in the dark: by emitting calls and listening to echoes. ![](Images/SAR.png) -Coincidentally, the radars on some missile defence batteries (such as the MIM-104 Patriot PAC-2) and other military radars operate using frequencies in the NATO G-band (4,000 to 6,000 Gigahertz) which overlaps with the civilian C-band (4,000, to 8,000 Gigahertz), commonly used by open source SAR satellites. +Coincidentally, the radars on some missile defence batteries and other military radars operate using frequencies in the NATO G-band (4,000 to 6,000 Gigahertz) which overlaps with the civilian C-band (4,000, to 8,000 Gigahertz), commonly used by open source SAR satellites. -In the simplest terms, this means that when the radar on the likes of a Patriot battery is turned on, Sentinel-1 picks up both the echo from its own pulse of radio waves, as well as a powerful blast of radio waves from the ground-based radar. This shows up as a stripe of interference perpendicular to the orbital pass of the satellites: +In the simplest terms, this means that when the radar on the likes of a Patriot battery is turned on, Sentinel-1 picks up both the echo from its own pulse of radio waves, as well as a powerful blast of radio waves from the ground-based radar. This shows up as a stripe of interference perpendicular to the orbital path of the satellite: ![](Images/RFI_localization_1.png) -Sentinel-1 works by illuminating a 250km long and 5km wide swath of land below the satellite with a pulse of C-band radio waves (shown as the red triangle). If interference is detected, its source (depicted as a yellow dot above) will be located somewhere within this swath. +Sentinel-1 works by illuminating a 250 kilometre (km) long and 5km wide swath of land below the satellite with a pulse of C-band radio waves. If a powerful ground-based radar creates interference, the entire 250-by-5 km swath in which it is located will be affected, creating a bright stripe in the image. Other military radars that operate on the same C-band frequency include naval radars such as the Japanese FCS-3, the Chinese Type-381 and the Russian S-400 Surface to Air Missile system. All should be detectable when switched on and in view of Sentinel-1.