VIIRS High Rate Data (HRD) Broadcast
NASA/GSFC Ground Receiving Station

About the VIIRS HRD Broadcast
The VIIRS High Rate Data (HRD) broadcast is analogous to the Aqua/Terra MODIS Direct Broadcast. Generally, a spacecraft collects and stores data on board until it passes over a ground station set up to receive the data, at which point the spacecraft transmits the data in one large batch. This avoids losing data taken when the spacecraft is out of sight of any ground stations, such as when it is over the ocean.

VIIRS stores data on board for later download, but it also broadcasts the HRD it collects immediately, on the chance that someone on the ground below is listening. NASA/GSFC has the antennas and other equipment necessary to receive and process VIIRS HRD whenever the spacecraft is above the horizon. The Overpass Predictor can be used to determine when there will be an SNPP or JPSS-1 spacecraft overpass of NASA/GSFC (Greenbelt, MD) or any other location that may have a VIIRS HRD receiving station.

About the Images
The VIIRS instrument takes data by scanning from side to side as it passes over the Earth. The instrument points straight down, and "sees" up to 56 degrees to either side. Because of this, the image is most accurate down the centerline of the image, and becomes more distorted (compressed) towards either side. This is a combination of the angle at which VIIRS is viewing the ground and the curvature of the Earth.

The images are built from multiple VIIRS bands that collect visible light during daytime, and infrared light at night. The images shown have a resolution of 1 kilometer per pixel at nadir (the picture centerline). The height depends on the length of the overpass, but generally exceeds 3600 pixels.