The Hudson River affords me the almost unique place to show this phenomenon of our Doppler Radar.

With this feature turned “On” moving objects coming towards us from any direction show up in RED. Moving objects that are moving away from us show up as GREEN.

There are long freight trains frequently passing on the west side of the Hudson River. Passenger trains traverse the east side, and they are generally shorter.

So what you see on the screen shot above are freight cars traveling toward us (RED), and some others, part of the same train, moving away from us (GREEN).

Below is a small BOAT heading south towards us;

After the boat passes, the Doppler Radar shows it as a green object on-screen.

Here is the Doppler Effect of a large freighter passing us in a narrow section of the Hudson.