Horizon Detection for Mars Surface Operations

A new image processing method for automated horizon
detection is presented in this paper. This method was
developed for the Mars Exploration Rovers mission’s surface
operations to aid in determining orbiter visibility periods for
downlink data, and is now being considered for all Mars surface
missions and for a variety of applications. Starting with images
received from Mars rovers or landers, the horizon pixel location
is found by (1) obtaining the gradient images using the Sobel
operator, (2) calculating the preliminary horizon locations by
optimizing the maximum difference between sky and ground regions
in the gradient domain, and (3) applying a multi-variable
thresholding method. The results are analyzed using a variety of
images from the Mars rovers, as an example one dataset’s results
were categorized as 94.2% Good, 4.11% Okay, and 1.65%
Poor. The pixel location corresponding to the found horizon
in an image is converted to azimuth and elevation values using
the camera model. The elevation of the terrain surrounding
the rover or lander directly affects the duration orbiters are
visible for downlink data volume, and when the sun is visible
for image quality or solar energy consumption. Having an
automated process to detect the elevation of the terrain allows
the operation team to better predict the outcome of the plan,
reducing heath and safety risks and allowing new operational
limits to be defined.