I. Subsurface drainage
2.1.5 Research and development
The research requirements of SAPHYDATA are those relating to the acquisition, pro- cessing, and dissemination of hydrologic data. In recent years the major national and international research in hydrologic data systems has been in the area of network design and processing of the data. Deficiencies exist at all levels of activity in the development of
Descrigtion of different systems Characteristics
new instrumentation and methodology for the acquisition of data and for dissemination of the data.
The advent of satellites with their broad synoptic cover of ground systems and rapid communication of data has encouraged hydrological service organizations to review existing data acquisition systems and to improve the instrumentation available so that it will communicate parallel to the data from satellite observation systems. Present data acquisition systems for hydrologic investigations were largely developed in the early part of the twentieth century. Certain improvements have been made in mechanization of certain phases of the system-digital recording, bubble gauges, etc.-but the fundamental principles remain essentially unchanged.
Immediately needed is more research in the measurement of stream velocity, depth and width for the computation of streamflow. Techniques are needed that willto some extent replace the elaborate stage-discharge relationships so that direct information may be obtained on stream discharge. Improvements should be made in the acquisition of water- quality data through the improvement in automatic recording of water quality and through sensing of water characteristics through aerial or satellite photography.
2.1.5.1
In Chapter 3 the principles of adaptation of existing technological capabilities for water- resource investigations will be reviewed and examples of the interchange of technology illustrated. The capacities for technological innovation are somewhat limited in the devel- oping countries, but every country has within its reach the basic components of the system. The only possible exception at this time is perhaps satellite observations, but even in this case the fruits of photography and imagery are generally available to the users.
Satellites are not generally flown for water-resource investigations and they willnot be in the near future. The problem is one of linking hydrologic data collection, observations, and possibly communication of data to systems flown for a variety of reasons and purposes.
For example, colour photography, infrared, and microwave imagery are general- purpose systems designed primarily for photomapping, inventorying agriculture resources, but with proper interpretation these images may be used to assess the water resources.
A significant amount of work has been done by several countries in the interpretation of information on aerial photographs and their relations to water-resource problems.
Space systems are now performing directly in the service of man. Their revolutionary contributions to meteorology and long-distance communications are widely known, and very significant advances have been and are being made with satellite systems in navigation and geodesy. The potential for additional uses of space technology for man’s immediate benefit seem vast.
Satellites possess performance characteristics that make them uniquely effective for earth reconnaissance and survey. These include unprecedented speed in orbit and extremely high altitudes for viewing. Cameras in satellites can compress a synoptic view into a single frame, or into several successive frames, showing relationships and activities over a large area at, in effect, a single moment in time, and in a format that can enormously simplify the handling of data. Repetitive coverage through successive orbital passes can record a ‘ time lapse’ history of changes, providing new insights into dynamic processes on the earth’s surface. Space techniques can also improve the effectiveness of traditional aircraft and ground surveying. The larger view provided by the satellite can direct, or
‘target’, the closer surveys with greater accuracy.
Imagery from satellites, as well as the excellent colour photographs taken with hand- held cameras during manned space flights, are accomplishments of the initial phases of the investigation of planetary surfaces from space vehicles. Some typical recent activities include the identification of ice types and charting of ice distribution in the Great Lakes
General consideration on remote sensing
and the St. Lawrence Seaway and the study of the distribution and changes of snow cover, using weather satellite photography
;
plans for magnetometer observations from space to obtain global coverage of three-dimensional information on the structure of the earth’s crust and clear and accurate delineation, for the first time, of the entire Gulf Stream, using infrared photographs taken on a single satellite pass.With the various kinds of imagery acquired by space platforms and the advanced methods of data handling now coming into use, researchers in the earth sciences will be confronted with unexpected discoveries. N e w insights and new orientations have already begun to emerge. Space-age technology and methods have begun to have an impact on methodology and training in the earth sciences, and this dynamic influence willcontinue.
Conversely, as they successfully demonstrate the effectiveness of remote sensing as an aid in solving problems associated with man’s needs on earth, scientists can exert some influ- ence on the character and scope of national space programmes and on the development of the associated instrumentation.
2.1.5.2
Remote sensing is the detection of the characteristics of an object without direct contact with it. The human eye is a remote sensor. Photography is remote sensing. Remote sensors may be ground based, airborne, or satellite-borne. Among the remote-sensing techniques that have been tested in hydrological work are near-infrared photography, far-infrared scanning, radar scanning, and ultraviolet scanning. In scanning methods the incoming signal may be manipulated electronically to produce an image resembling a photograph.
It is anticipated that at some future time certain kinds of basic hydrological data willbe obtained routinely by remote sensing instruments that will feed the data into automated systems.
Most remote sensing for hydrological purposes is still in the experimental and develop- mental stages. Ground-based radar, however, has been perfected long since for routine detection of where and when precipitation is occurring. Use of the technique to measure rates of rainfall, on the other hand, has yielded variable results, commonly differing by as much as 75 per cent from rates indicates by standard rain-gauges.
Owing to the high spatial variability of rainfall in local and orographic storms, some estimates of area averages based on classical point measurements have doubtful validity.
It would be extremely useful to have a dependable sensing technique, especially for remote areas that are difficult of access. Recent studies of the state of the art of using radar to estimate rainfall distribution and intensity show that the technique has little operational application at present and then only in flat terrain. Problems to be resolved include the theoretical basis of the method, improvement of basic equipment, and effective data reduction.
Airborne infrared sensing has proved its practical usefulness for mapping submarine springs, classifying and mapping vegetation, detection of mixing and dispersion patterns in water bodies, and other purposes. It has also been tested for the mapping of areas actually wetted by rainstorms in arid areas.
For topographic and geologic mapping remote sensing from airplanes is quite feasible because geology and topography do not change rapidly. For hydrological parameters that are constantly changing, airborne sensing is still very expensive because each resurvey costs as much as the first. For this and other reasons hydrologists have studied and experi- mented with sensors to be borne in orbiting satellites. The initial cost is high but repeat surveys cost very little. Satellites have the advantage that they can provide repetitive data for given areas. Much work with aircraft has been aimed at development and testing of instruments for use in satellites.
Excellent summaries have been published recently (Fischer, 19680, 1968b, 1968c;
Popham, 1968 ; Baker and McClain, 1970; Kondrat’ev, Borisenkov and Morozkin, 1966;
Remote sensing application to hydrology
Description of different systems characteristics
Kmito, 1966; Kondrat'ev and Timofeev, 1970) on the state of the art of remote sensing, along with selected bibliographies of useful references.
A n orbiting satellite may also carry a communications device which can interrogate ground-based instruments and transmit their information to an information centre or system.
Glaciers are among the most inaccessible of land areas. Repetitive surveying of snow and ice areas by land-based methods is very costly and time consuming. Successful devel- opment of remote-sensing methods would permit surveys and inventories at reasonable cost and thus aid greatly in inventories of water storage and predictions of water yield.
Airborne remote-sensing tests over some large glaciers have had encouraging results (Meier and others 1966; Kondrat'ev and others, 1966).