[1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.

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The Shuttle Radar Topography Mission

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

A classification of channel-reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types: colluvial, bedrock, and five alluvial channel types (cascade, step pool , plane bed, pool rime, and dune ripple). Coupling reach-level channel processes with the spatial arrangement of reach morphologies, their links to hillslope processes, and external forcing by confinement, ripar­ ian vegetation, and woody debris defines a process-based framework within which to assess channel condition and response potential in mountain drainage basins. Field investigations demonstrate character­ istic slope, grain size, shear stress, and roughness ranges for different reach types, observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad­ justed to the relative magnitudes of sediment supply and transport ca­ pacity. Steep alluvial channels (cascade and step pool) have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply, whereas low-gradient alluvial channels (pool rime and dune ripple) have lower transport capacity to supply ra­ tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge. General differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source, transport, and response segments, the spatial distribution of which provides a watershed-level conceptual model linking reach morphology and channel processes. These two scales of channel network classification define a framework within which to in­ vestigate spatial and temporal patterns of channel response in moun­ tain drainage basins.

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Channel-reach morphology in mountain drainage basins

Elevation data is vital to successful mission planning, operations and readiness. Traditional methods for producing elevation data are very expensive and time consuming; major cloud belts would never be completed with existing methods. The Shuttle Radar Topography Mission (SRTM) was selected in 1995 as the best means of supplying nearly global, accurate elevation data. The SRTM is an interferometric SAR system that flew during 11-22 February 2000 aboard NASA's Space Shuttle Endeavour and collected highly specialized data that will allow the generation of Digital Terrain Elevation Data Level 2(DTED® 2). The result of the SRTM will increase the United States Government's coverage of vital and detailed DTED® 2from less than 5% to 80% of the Earth's landmass. This paper describes the shuttle mission and its deliverables.

The longitudinal profiles of bedrock channels are a major component of the relief structure of mountainous drainage basins and therefore limit the elevation of peaks and ridges. Further, bedrock channels communicate tectonic and climatic signals across the landscape, thus dictating, to first order, the dynamic response of mountainous landscapes to external forcings. We review and explore the stream-power erosion model in an effort to (1) elucidate its consequences in terms of large-scale topographic (fluvial) relief and its sensitivity to tectonic and climatic forcing, (2) derive a relationship for system response time to tectonic perturbations, (3) determine the sensitivity of model behavior to various model parameters, and (4) integrate the above to suggest useful guidelines for further study of bedrock channel systems and for future refinement of the streampower erosion law. Dimensional analysis reveals that the dynamic behavior of the stream-power erosion model is governed by a single nondimensional group that we term the uplift-erosion number, greatly reducing the number of variables that need to be considered in the sensitivity analysis. The degree of nonlinearity in the relationship between stream incision rate and channel gradient (slope exponent n) emerges as a fundamental unknown. The physics of the active erosion processes directly influence this nonlinearity, which is shown to dictate the relationship between the uplift-erosion number, the equilibrium stream channel gradient, and the total fluvial relief of mountain ranges. Similarly, the predicted response time to changes in rock uplift rate is shown to depend on climate, rock strength, and the magnitude of tectonic perturbation, with the slope exponent n controlling the degree of dependence on these various factors. For typical drainage basin geometries the response time is relatively insensitive to the size of the system. Work on the physics of bedrock erosion processes, their sensitivity to extreme floods, their transient responses to sudden changes in climate or uplift rate, and the scaling of local rock erosion studies to reach-scale modeling studies are most sorely needed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JB900120

Dynamics of the stream‐power river incision model: Implications for height limits of mountain ranges, landscape response timescales, and research needs

Stripping of the vegetation and soil from a 13-hectare site in Virginia underlain by coastal plain sediments created a rapidly evolving badland topography. Two types of channels developed: (1) sand-bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff, but they also generally eroded their beds slowly, and (2) steeper, bedrock-floored channels incised rapidly. In bedrock channels the erosion rate was proportional to the 4/9ths power of drainage area and the 2/3rds power of gradient. These exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows. Due to rapid mass wasting and reduced runoff, the alluvial channels became as much as 50% steeper during the winter than the summer, with an attendant yearly cycle of winter aggradation and summer entrenchment. The gradients, their seasonal variability, and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads. The hydraulic geometry of alluvial channels in the Virginia badlands were similar to that on the Morrison Formation in the western United States.

Gordon Kerby

Papers

Channel changes in badlands