## Appendix A The MISR Instrument and MISR-HR Products
### The MISR-HR Processing System  
Land surfaces often exhibit significant heterogeneity at scales finer than the spatial resolution of standard MISR products (1100 m). Other instruments operating during the same period, such as the NASA Landsat program or the CNES SPOT instrument, deliver imagery at finer spatial resolutions but offer a lower revisit frequency because of their narrow swath width; they also lack the ability of systematically acquiring multi-angular observations. Recently, the trend towards finer and finer spatial resolutions has led to ever more limited spatial coverage (for engineering reasons), and stimulated the operation of constellations of satellites to remedy this problem. However, the interpretation of data products generated by very high spatial resolution instruments (e.g., at sampling distances commensurate with the size of the objects in the scene, such as trees) is very complex, as it requires radiation transfer models that represent the scene with that amount of detail. The MISR-HR (for High Resolution) processing system [46] is designed to deliver a suite of land surface products at the native spatial resolution of 275 m, which is finer than the standard MISR products but nevertheless coarse enough to allow the use of classical (e.g., two-stream) radiation transfer models. This processing system requires four standard MISR data products as input:  
1. The Ancillary Geographic Product (Earth Science Data Type or ESDT identifier: MIANCAGP) contains information on the latitude, longitude, and altitude distribution of each Block within the corresponding Path, as well as a scene classifier, for each 1100 m pixel, on the SOM map projection grid. 2. The Geometric Parameters Product (ESDT identifier: MI1B2 GEOP) contains information on the applicable illumination and observation geometry (zenith and azimuth angles), as well as the scatter (angular distance between the Sun and camera directions) and glitter (angular distance to specular reflection) angles for each of the 9 cameras. 3. The L1B2 Terrain-projected Product (ESDT identifier: MI1B2T), in either Global or Local Mode, contains the calibrated Georectified Radiance Product (GRP) values measured by the MISR instrument, i.e., at the nominal 'Top of the Atmosphere' (ToA). 4. The Level 2 Land Product (ESDT identifier: MIL2 ASL) contains the standard MISR Level 2 Land products, at the nominal 'Bottom of the Atmosphere' (BoA), i.e., after taking into account the contribution of the atmosphere to the observed radiance. The MISR-HR processing system (currently at Version 2.01) proceeds through six steps to generate four sets of output products:1. The first step consists in replacing missing values in the MISR L1B2 GRP, as well as in the Radiometric Camera-by-Camera Cloud Mask (RCCM) data sets, as described in [112; 113]. These intermediary products are currently not saved but used directly in the subsequent steps. 2. A sharpening algorithm is then applied to this updated L1B2 GRP product to generate the L1B3 product, i.e., the 36 bidirectional spectral reflectance data channels at the nominal Top of the Atmosphere (ToA), at the full spatial resolution of the instrument (275 m). This product resembles the MISR Local Mode product, except that (1) it can be generated everywhere (and does not depend on Local Mode acquisitions), (2) the data values in the 24 non-red, off-nadir data channels are obviously reconstructed (since the only available observations are at the spatial resolution of 1100 m), and (3) the swath width of the L1B3 product does not exceed that of the nadir camera since the latter is used in this reconstruction. 3. An algorithm is then applied to the L1B3 product to estimate the bidirectional spectral reflectance factor (BRF) of the surface, sometimes also called Bottom of the Atmosphere (BoA) reflectance. This process takes into account the contribution of the atmosphere itself to the original measurements and yields 36 data channels at the native spatial resolution of the instrument. 4.