I am working on MISR and MODIS Level-2 data, compare these two dataset with ground measurements: I found better correlation with MISR than MODIS, and MODIS also over estimate MISR . I also found in literature MISR AOD is better than MODIS because it use the multiangle (9 angles) at the time of image acquisition.Here my question is that how does multi-angle increase the accuracy of MISR?
The sensitivity to aerosol is increasing with increasing of view angle because we look through larger amount of atmosphere. For example MISR C-cameras look through twice larger amount of atmosphere than just a nadir view. So this allows to retrieve more information about aerosol (i.e. different aerosol particle types) and better constrain models for aerosol retrieval. MISR allows more accurate retrieval (including AOD) especially over heterogeneous landscapes or dense forests.
The sensitivity to aerosol is increasing with increasing of view angle because we look through larger amount of atmosphere. For example MISR C-cameras look through twice larger amount of atmosphere than just a nadir view. So this allows to retrieve more information about aerosol (i.e. different aerosol particle types) and better constrain models for aerosol retrieval. MISR allows more accurate retrieval (including AOD) especially over heterogeneous landscapes or dense forests.
Maxim's response is absolutely correct. I would expand on it as follows:
- On any particular day (i.e., for quasi-instantaneous observations), MODIS can only rely on the spectral signature of the atmosphere to infer aerosol properties. I don't remember how many channels are actually used in this process, but let's say it is about a dozen or so in the visible to near-infrared range.
- Under the same conditions, MISR will use both spectral and directional observations to pursue the same goal. Since there are 9 cameras at different angles, and each features 4 spectral bands, there are 36 data channels available for analysis.
- The key point is not only that at some angles (like 60 degrees), the sensor samples twice the atmospheric depth, but also that aerosols themselves have strong anisotropic response (called the phase function). Hence, observing them from different angles helps assess the optical depth (amount) but also their optical properties and chemical composition (to some extent).
- Also note that polarized measurements (currently planned for future missions such as MSPI and Glory) will provide even more and better information on atmospheric aerosols.
- There is ample literature on this topic, and you'll find a comprehensive list of bibliographical references on MISR from the following web pages:
https://www-misr.jpl.nasa.gov/publications/peerReviewed/
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