DINO Stereoscopic Imaging Overview
Purpose:
1. Summarize all relevant articles and ensure a common knowledge base among the
team.
2. Propose several solutions to problems presented in the DINO Science Overview
document.
3. Present areas of further research.
Summary:
 Stereoscopic viewing requires at least two different viewpoints of a common
object.
 Height determination of cloud tops requires knowledge of “y” parallax and the
angles of the cameras given by the formula:
Height =
“y” parallax
.
Tan (foreword camera angle) – Tan (nadir camera angle)
With “y” parallax compensated for wind along the track of the satellite
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When determining cloud height, the base to height ratio (b/h) of the right triangle
should be large to reduce the height errors incurred by errors in satellite position.
The b/h ratio is determined by the magnitude of the forward looking camera angle
and increases the time between photographs as the angle increases from the nadir.
o Consequently, while a large b/h ratio is desired, a long time delay between
pictures is not.
o For the MISR satellite there was a 95% chance of successfully
determining cloud height for adjacent cameras which reduced to 78%
when a 70.5 degree angle between foreword looking and nadir camera was
used.
o This reduction in success is due to larger changes in illumination,
refractive effects, and temporal changes between pictures.
Causes of Errors
o Unknown platform position, velocity, and orientation.
o Errors in the manufacturing of the cameras.
o Errors in the projection of the stereoscopic image.
o Cloud drift.
Storm cloud height ranges from 50,000 feet over the middle latitudes to 60,000
feet near the equator. The radius of the top of the cloud reaches up to dozens of
miles depending on how developed the storm cloud is.
Solutions to Common Problems:
1. What is the positional knowledge of DINO?
a. We receive position information every two weeks from NORAD and have
equations for determining position during the intervals. Additionally
DINO’s cameras can be used to update and check the equations’ accuracy
(fig.1).
2. The ideal angle between foreword looking and nadir cameras are dependant on
the accuracy of positional knowledge and camera layout.
a. Figure 2 gives information regarding accuracy versus camera angle for the
MISR satellite. I would expect our accuracy to be less. If the use of a
panoramic camera is feasible it would be wise to decrease the angle
between nadir and foreword after the satellite’s position has been recently
obtained and increase the angle as the satellite’s position becomes more
unknown.
3. What are the major algorithm types?
a. Most satellites seem to be using a form of the least squares method to
determine cloud heights.
4. Will more pictures help?
a. They will help reduce the effects of cloud drift and increase accuracy of
the topographical map, but only if the pictures are at different angles
relative to nadir. Additionally, weather data could provide useful
information including:
i. Wind speed and direction
ii. Areas of cloud layers
iii. Estimated Cloud height
Areas of Further Research
 How autonomous should DINO be?
o Weather data is useful in predicting events for six hours after it is
forecasted. We could find an area crossing DINO’s orbit of clouds of
appropriate size using weather forecasts. Then DINO could reaffirm its
position as described above while mission control inputs constraints for
cloud height along with the speed and direction of the cloud. DINO would
take its topographical map at the precise point we tell it; there would be no
need for the processor to decide if the picture is usable because we could
have the satellite take a stereoscopic picture at a predetermined boundary
point and the resulting elevation data would be accurate due to calibration
of DINO’s position and geometric constraints of cloud height.
 What is a Wallis filter?
 Can the matching algorithm handle illumination differences between points?
 How does the least squares method work?
 Why are ground reference points needed?
Fig. 1
DINO takes pictures of two points along its orbit with a known distance between them. If
the landmarks show up within the center of the pictures then the equations are perfect.
Should the points not center, then we would know how much and in what directions our
equations regarding DINO’s speed and track err and can correct them.
DINO can check its height by taking a foreword looking picture at a known landmark
and then a nadir pointing picture of the same point. We know the distance between the
two pictures and the angle θ. From this we can derive height above the known point
using the equation:
H=
x
Tan(θ)
.
Given the known height above sea level of the location we can easily figure out DINO’s
altitude and see if the equations need adjusting.
Fig. 2
View angle
+70.5 +60.0 +45.6 +26.1 0.00 °
Absolute accuracy for height
515
1,462 8,713 393
1,286m
(This table was written in British so someone might want to validate my conversion, just
ask for a link to the file)