# Presentation: 388221

## MISR Geo-registration Overview

**Brian E. Rheingans**
**Jet Propulsion Laboratory, **
**California Institute of Technology**
**AMS Short Course on Exploring and Using MISR Data**
**Long Beach, California**
**9 February 2003**

## MISR Background

**Four MISR images over Appalachain Mountains**
**Nadir, 45.6 deg, 60.0 deg, 70.5 deg forward viewing cameras**
**To make use of angular as well as spectral information all**
** ****(9 cameras X 4 bands = 36) pixels must be accurately co-registered**

## MISR Background

**Each MISR camera eventually**
**Views one ground point at a**
**Slightly different time from a**
**Different angle as the spacecraft**
**Passes over that point.**
**Data is resampled from each channel**
**Onto a common map projection,**
**Called Space Oblique Mercator**
**(SOM).**

## SOM Background

**The Space Oblique Mercator **
**(SOM) map projection was**
**developed to support LandSat**
**which covers the same**
**large geographic extent as**
**MISR.**
**SOM was designed to minimize**
**the shape distortion and scale**
**errors throughout the length **
**of the MISR swath near the**
**satellite ground track.**

## SOM Background

**Terra follows a pattern of orbits which repeats after 233 unique orbits**
**Each of the 233 possible orbits is called a path**
**SOM defines a separate projection for each of these paths**
**For MISR, a path begins at a particular longitude as the satellite**
** ****crosses the ascending node.**
**This path implies a specific longitude of ascending node, which implies**
** ****a specific SOM projection applicable to that path**

## MISR Orbital Paths

## SOM Background

**SOM coordinates are X,Y in meters**
**X axis points in the approx. direction of the satellite groundtrack**
**Y axis is perpendicular to the X axis**
**The origin of X is at the ascending node equator crossing**
**Once ascending node is reached, X values start over at 0 for the next path/proj.**
**The sign of Y is relative to the sinusoidal X axis**

## SOM Background

**Line/Sample**
**Pixels are arranged in a regular 2-D array in SOM space**
**The indices are absolute line and sample**
**Given the SOM(X,Y), pixel resolution, and absolute line/sample offset**
**  ****you can compute the SOM coordinate of any other point in the swath**
**Blocks**
**MISR path is cut-up into a series of pre-defined, uniformly-sized SOM**
** ****boxes along the ground track, called blocks**
**For MISR, block-relative lines and samples restart at 0,0 at the top**
** ****left of each block and thus MISR has a block number**
**MISR files are ****BLOCK-RELATIVE****, not absolute.**

## HDF-EOS Background

**Grid**
**All MISR products are in HDF 4 format**
**HDF-EOS  = HDF 4 + GCTP**
**HDF-EOS data type for map projected data is called “Grid”**
**HDF-EOS Grid metadata stores orbital parameters and map**
** ****projection parameters**

**“****Stacked Block” Grid**
**Problem was MISR data (w/ large extent) didn’t fit the Grid model**
**Extension to the grid model to store MISR blocks**
**Actually, it is a 3-D array (block, line, sample)**
**Blocks are stack on top each other with a constant vertical offset (1 block)**
**The lateral offset is not constant**

## HDF-EOS Background

**Block Offset**
**Blocks may be shifted left or right by an integral multiple of 17.6 km**
**Shifts are pre-defined, as is the block locations to encompass MISR footprint**
**MISR stack-block grid is defined for a given path by the coord. of the first**
**  ****block, along with standard projection metadata and an array of block offsets**
**  ****to define the locations of all subsequent blocks.**

## HDF-EOS Background

**HDF-EOS routines do NOT assemble the**
**Blocks.  That is left for the user.**
**180 blocks are defined for every MISR**
**Product to make block index in absolute.**
**However, roughly 142 blocks have data for**
**Any given orbit.  The extra blocks are to**
**Allow for seasonal variation.**

## MISR Product Characteristics

**MISR L1B2 and above product characteristics:**
**Space Oblique Mercator (SOM) map projection**
**Stacked-block HDF-EOS Grid format**
**Large geographic extent**
**Determining latitude and longitude of a MISR pixel (2 methods):**
** ****1) Look up in Ancillary Geographic Product (AGP)**
**One AGP for each Terra orbital path**
**Separate product**
**Stored at 1.1km**
** ****2) Convert coordinate systems**
**Orbital param. and projection info. are in all MISR products**
**HDF-EOS library access routines used to read metadata**
**GCTP map projections library used (w/ HDF-EOS)**
**Algorithm to map between SOM(X,Y) and  MISR(b,l.l,s.s)**
**See Appendix A of the MISR DPS**

## Coordinate Conversions

**Forward Conversion:**
**Lat/Lon -> SOM(X,Y) -> MISR(b,l.l,s.s)**
**Useful for resampling MISR data to another projection**
**Notice line and samples can be fractional**
**Inverse Conversion:**
**MISR(b,l.l,s.s) -> SOM(X,Y) -> Lat/Lon**
**Useful for determining lat/lon of a pixel**
**Orbit path must be known a priori (metadata is required)**
**	**
**Coordinate conversions are reversible with reasonable numerical**
**  ****Precision only for positions near the satellite ground track.**
**Positions not near the ground track are better-described on another**
**  ****Path and SOM projection.**

## SOM <-> Lat/Lon

**Forward: Lat/Lon -> SOM**
**Given a pixel’s position in Lat/Lon coordinates assuming a particular**
**  ****MISR orbit path, SOM(X,Y) in meters can be computed by:**
**Retrieving projection parameter metadata.**
**Calling SOM forward routines from the GCTP library.**

**Inverse: SOM -> Lat/Lon**
**Given a pixel’s position in SOM(X,Y) meters, assuming a particular**
**  ****MISR orbit path, Lat/Lon can be computed by:**
**Retrieving projection parameter metadata**
**Calling SOM inverse routines from the GCTP library.**

## MISR(b,l.l,s.s) -> SOM(X,Y)Inverse Conversion

## SOM(X,Y) -> MISR(b,l.l,s.s)Forward Conversion

## Coordinates in other Map Projections

**Forward:**
**AnyProj(X,Y) -> Lat/Lon -> SOM(X,Y) -> MISR(b,l.l,s.s)**
**Useful for reprojecting to another map projection**

**Inverse:**
**MISR(b,l.l,s.s) -> SOM(X,Y) -> Lat/Lon -> AnyProj(X,Y)**

## Interrupted Goode Homolosine

## Geometric Parameters Product

**The following**
**Parameters are**
**Stored in the **
**Geometric Product**
**(GMP):**

**View Zenith**
**   ****per camera**
**View Azimuth**
**   ****per camera**
**Solar Zenith**
**Solar Azimuth**
**Scatter Angles**
**  ****per camera**
**Glitter Angles**
**  ****per camera**