Satellite Gravimetry Applied to Drought Monitoring

Near-surface wetness conditions change rapidly with the weather, which limits their usefulness as drought indicators. Deeper stores of water, including root-zone soil wetness and groundwater, portend longer-term weather trends and climate variations, thus they are well suited for quantifying droughts. However, the existing in situ networks for monitoring these variables suffer from significant discontinuities (short records and spatial undersampling), as well as the inherent human and mechanical errors associated with the soil moisture and groundwater observation. Remote sensing is a promising alternative, but standard remote sensors, which measure various wavelengths of light emitted or reflected from Earth's surface and atmosphere, can only directly detect wetness conditions within the first few centimeters of the land s surface. Such sensors include the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) C-band passive microwave measurement system on the National Aeronautic and Space Administration's (NASA) Aqua satellite, and the combined active and passive L-band microwave system currently under development for NASA's planned Soil Moisture Active Passive (SMAP) satellite mission. These instruments are sensitive to water as deep as the top 2 cm and 5 cm of the soil column, respectively, with the specific depth depending on vegetation cover. Thermal infrared (TIR) imaging has been used to infer water stored in the full root zone, with limitations: auxiliary information including soil grain size is required, the TIR temperature versus soil water content curve becomes flat as wetness increases, and dense vegetation and cloud cover impede measurement. Numerical models of land surface hydrology are another potential solution, but the quality of output from such models is limited by errors in the input data and tradeoffs between model realism and computational efficiency. This chapter is divided into eight sections, the next of which describes the theory behind satellite gravimetry. Following that is a summary of the GRACE mission and how hydrological information is gleaned from its gravity products. The fourth section provides examples of hydrological science enabled by GRACE. The fifth and sixth sections list the challenging aspects of GRACE derived hydrology data and how they are being overcome, including the use of data assimilation. The seventh section describes recent progress in applying GRACE for drought monitoring, including the development of new soil moisture and drought indicator products, and that is followed by a discussion of future prospects in satellite gravimetry based drought monitoring

A Sprig of Rosemary for Hammy

Magic was the word for Walton Hamilton, who died this past October, seventy-seven years young. There was magic in his manner of teaching—no rigid laying out of rules, no question-and-answer quiz show, no cat-and-mouse sparring with students with the mouse predoomed to defeat. Rather, the subtle inference that sank in slowly, the oblique suggestion like a sign-post dimly seen at dusk and hence far better remembered; he might be called the precursor of the hidden persuaders, except that he had nothing to sell save his own warm-wise way of looking at law and the world. There was magic too in his manner of writing—the soft stab, the tangential epigram that had to be read twice and then yielded ten times its surface meaning; his every line of prose was imbued with latent poetry. And there was magic in the manner of man he was—a gentle southerner out of Tennessee whose shuffling bounce belied his inner firmness but betrayed his outer shyness, a Carl Sandburg sort of man in humor and simplicity, a man whose intellectual questings and excitements brushed off on everyone he taught or knew. Hammy and I came to the Yale Law School together in the fall of 1928, just thirty years ago—and though he came as professor, I as student, we had one thing in common: neither of us had ever been to a law school before. He had taught in secondary schools and at the Universities of Texas and Michigan and Chicago; he had taught at Amherst (and quit when its president, his close friend Alexander Meiklejohn, was fired) and at the Brookings School in Washington; he had taught medieval history and economics and something called political economy. He had never taught, or formally studied, law

A Primer on Interstate Taxation

Picture a map of the United States. Each state is marked out in red or yellow or green or orange, in between the blue that is saved for the oceans and the dull white of Mexico and Canada. Now imagine a series of walls ten miles high running along the boundaries of each block of color and shutting every state off from the states around it. It will be helpful to remember that problems of interstate taxation are treated by the law very much as though those imaginary walls were real. Now the average man knows well enough what a tax is. It is a sum of money that must be paid to a government because the payer owns something or does something or gets something. If the tax is on anything it is on the man or the company that must pay the tax. Sometimes the tax is a flat tax, like a two dollar school tax that must be paid by everyone who lives in the school district. More often the amount of the tax is measured according to the value of whatever the taxpayer owns or does or gets that makes him have to pay the tax. So much seems sufficiently simple