remote sensing in hydrology

Remote Sensing In Hydrology ADITYA A. PUNGAVKAR ROLL NO: 09 AR 6017 MCP 1ST YEAR

Remote sensing in hydrology

Aditya A. Pungavkar. Roll No:09AR6017 MCP 1ST Year.

Remote sensing in hydrology.

An adequate and continuous supply of water for drinking, agriculture, and industry is basic for all societies.

Significant deviations from normal water supplies generally bring disaster in the form drought or flood. to

avoid the problems resulting from excess and shortage of water, societies have invested enormous sums of

money and employed hydrologists and civil engineers to develop systems to control and distribute water.

With nearly three-quarters of the earth being covered with oceans. It is not a question of a global shortage of

total water, but the challenge is to overcome the uneven distribution of water in space and time on land areas

and to supply adequate quality to meet local needs. for example, about 20 per cent of the earth`s land area is

classified as arid and an additional 15 per cent is classified as semiarid. Here, water has been the limiting

factor in the development of agriculture and most industries. Yet, even these dry areas are periodically

devastated by floods. The requirement placed on technology is to supply, at an affordable cost, a dependable

supply and quality of water where and when it is needed. Systems to control water supplies have consisted of

wells, canals, levees, and dams because available information is almost always inadequate, wells have been

dug that fail to produce adequate quantities or quality of water, dams have leaked or totally failed and waste

waters have contaminated drinking water. These disappointing results could have been avoided if sufficient

hydrologic, geologic and climatelogic information for resource planning had been available. The purpose of

this paper to view general capabilities of remote sensing techniques to obtain hydrologic data and to examine

remote sensing as a possible aid in operational hydrology in the future.



The hydrological cycle

a brief overview of hydrological processes will help to set a framework ford escribing those areas where

remote sensing can assist in observing and in managing water resource system. generally speaking, the

hydrological cycle traces water through different physical processes, from liquid water through evaporation

into the atmosphere, back into the liquid (or sometimes the frozen) state as precipitation falling on land areas

may either run off into rivers and streams, or percolate into the soil, or evaporate. moisture reaching the

water table becomes ground water. as a general rule, both surface and ground water flow under the force of

gravity toward streams and lakes, and ultimately oceans. The return of water to the oceans can thought of as

completing the cycle.

Precipitation

Accurate measurement of precipitation is a continuing goal in meteorological research and a continuing need

in hydrology which depends greatly on these data for modeling. Ground-based radar is probably the most

accurate method of determining a real precipitation in use today. Satellite images from GOES, NOAA,

TIROS-N, TRMM.

Introduction

Hydrology is a science built on observations and measurements. Operational hydrology and water resources

engineering have utilized these measurements for the design and operation of water resource systems and the

forecasting of hydrologic systems. There has been a long recorded history of hydrologic data collection in

support of operational hydrology going back to ancient chinese and egyptian times. in modern industrialized



countries, hydrologic data collection has focused on stream flow, precipitation and basic surface

meteorological data which are sufficient for the design and forecasting needs of the water resource engineers:

primarily the design of water supply and flood protection works, which requires long- term records for river

flows, and the forecasting of floods, which requires (spatially) accurate precipitation measurements. to fully

understand the data needs for operational hydrology, consider the primitive water balance equation

ds/dt = p - e - q

where (ds/dt) is is the change in soil moisture over a specified time interval, p is precipitation, e represents

evapotranspiration which is the sum of evaporation from bare soil, £#, and transpiration from vegetation, ey,

and q is runoff which is the [sum of surface, or direct storm runoff and subsurface or base flow. for water

supply and/or flood protection design where long-term reliability is critical, the dynamics of eq. are

unimportant. thus, the important measurements are time [•series of runoff and possibly precipitation, and a

climatological estimate of monthly evapotranspiration. changes in soil moisture over the long-term are

assumed zero. similarly, for flood forecasting, evaporation can be ignored, soil i moisture is only relevant to

the extent that initial abstractions (or losses) can be implemented, and river flow to the extent that

comparisons can be made between forecasts and observations

Remote sensing potentially may provide the required inputs for hydrological modeling at regional to global

scales. As a result, remote sensing initiatives have included field experiments (e.g. the first international

satellite land surface climatology field experiment, fife) that have linked ground measurements with remote

sensing algorithm development. in addition, there are now consistent, long-term remote sensing data archives

from satellites such as AVHRR (agbu, 1993), goes (young, 1995) and SSMI (hollinger et al., 1992).

by the late 1990's new and enhanced meteorological satellites and higher spectral resolution land surface

sensors being launched under NASA'S earth observing system mission, combined with faster computer

networking and data handling capabilities, will give operational hydrologists access to new types of land

surface and hydrologic data. in the second part of this chapter, we discuss the potential for utilizing these

data for hydrological modeling.



Remote sensing in operational hydrologic modeling

Runoff.

Cannot be directly measured by remote sensing techniques. how-ever, there are two general areas where

remote sensing can be used in hydrologic and runoff modeling: (1) determining watershed geometry,

drainage network, and other map-type information for distributed hydrologic models and for empirical flood

peak, annual runoff or low flow equations; and (2) providing input data such as snow cover, soil moisture or

delineated land use classes that are used to define runoff coefficients.

Watershed geometry.

Remote sensing data can be used to obtain almost any information that is typically obtained from maps or

aerial photography. in many regions of the world, remotely-sensed data, and particularly LANDSAT tm or

spot data, are the only source of good cartographic information. drainage basin areas and stream networks are

easily obtained from good imagery, even in remote regions. there have also been a number of studies to

extract quantitative geomorphic information from LANDSAT imagery (haraltck, et al., 1985).

Topography is a basic need for any hydrologic analysis and modeling. Remote sensing can provide

quantitative topographic information of suitable spatial resolution to be extremely valuable for model inputs.

for example, stereo spot imagery can be used to develop a dem with 10 m horizontal resolution and vertical

resolution approaching 5m in ideal cases (case, 1989). a new technology using interferometric synthetic

aperture radar (SAR) has been used to demonstrate similar horizontal resolutions with approximately 2m

vertical resolution (zebker et al., 1992).

Empirical relationships.

Empirical flood formulae are useful for making estimates of peak flow when there is a lack of historical

streamflow data. generally these equations are restricted in application to the size range of the basin and the

climatic tiydrologic region of the world in which they were developed.

most of the empirical flood formulae relate peak discharge to the drainage area of the basin; see for example

united nations flood control series no. 7 (united nations, 1955). LANDSAT data are used to improve

empirical regression equations of various runoff characteristics. for example, allord and scarpace (1979) have



shown how the addition of LANDSAT-derived land cover data can improve regression equations based on

topographic maps alone.

Runoff models

One of the first applications of remote sensing data in hydrologic models used landsat data to determine both

urban and rural land use for estimating runoff coefficients (jackson et al., 1976). Land use is an important

characteristic of the runoff process that affects infiltration, erosion, and evapotranspiration. Distributed

models, in particular, need specific data on land use and its location within the basin. most of the work on

adapting remote sensing to hydrologic modeling has involved the soil conservation service (SCS) runoff

curve number model (U.S. department of agriculture, 1972) for which remote sensing data are used as a

substitute for land cover maps obtained by conventional means (jackson a.u.1977, bondelid et al., 1982).

Integration with GIS

The pixel format of digital remote sensing data makes it ideal for merging with geographical information

systems (GIS). Remote sensing incorporated into the system in a variety of ways: as a measure of land use,

impervious surface for providing initial conditions of flood forecasting, monitoring of flood areas, rainfall

distribution or soil moisture. This approach was demonstrated by kouwen .et.al.

Soil moisture

Here continues to be speculation about the potential value for soil moisture data as in input variable in

hydrologic models, either to establish the initial conditions for simulating storm runoff, or as a descriptor of

hydrologic processes and much progress is beginning to appear as some of the aircraft experimental data

become available.

Soil water storage capacity.

All hydrological catchment models, rainfall-runoff models as well as water balance models contain a

component dealing with the soil water storage process. As long as there are difficulties to measure soil water

storage by remote sensing directly a substitute is often used, which uses remote sensing information coupled

with other information for the determination of the soil water storage capacity. If this is known, the soil water

storage process in time and space can be simulated.



Modeling example: the red river Arkansas basin: we illustrate the remote sensing approach outlined

above over the red river Arkansas basin. the Arkansas and red rivers head on the eastern slope of the rocky

mountains and flow to the Mississippi river near little rock, and Shreveport, la, respectively. The modified

variable infiltration capacity model (vic-3l) (Liang et al. 1994, 1996a,b), was used to estimate the water and

energy fluxes for the month of June 1987.

a summary of the June, 1987 basin average energy balance result for the hydrologic model runs is presented

in table the increased incoming radiation or the remotely-sensed forcing causes generally higher surface

energy fluxes. The vast majority of this increased net incoming energy is partitioned to the sensible beat flux.

color plates b, c and table show the spatial variations in the components of the energy balance over the

basin* part (a) shows the energy fluxes using the ground based forcing data; part (b) shows the fluxes using

the remotely-sensed forcing data and (c) shows the normalized percent difference between part (a) and part

(b). on the basis of this information computation of evapotranspiration becomes feasible.

Modeled basin average energy fluxes in w/nr for June 1987 using ground based meteorological forcing and

remotely-sensed forcing

net radiation latent heat sensible heat

ground based forcings remotely-

sensed forcings

190

242

106

112

81 125



a)

b) c)



Water management

Water management deals with the control, distribution and allocation of water flows and the treatment of

rivers and catchments, consequently, solutions too many of the problems in water management require the

use of knowledge and expertise from diverse sources. Some parts of these problems might best be solved

using traditional approaches like hydrologic measurement, monitoring or simulation modeling. Other

components may require information from one or more data bases from different domains such as

population, law, politics, economic statistics and biophysical resources. Many problems in water resources

management are however solved by qualitative reasoning and experience.

a common aspect in the many facets of water management studies is the location of the problem, the position

within the catchment and the spatial interrelationships between physical catchment characteristics, land use,

settlements and infrastructure. Aerial photography and satellite imagery contain spatial information of the

surface and near surface features of the earth to be captured and analyzed. Various imaging satellite sensors

are nowadays available. Remotely sensed image analysis, when applied to hydrology is best embedded in a

geographic and hydrologic information system (HGIS). a HGIS which can be thought of as a system

coupling the following elements: data bases, i.e. thematic, spectral images and hydrologic time series data, a

spatial analysis module with eventually a link to hydrologic simulation models or a rule base, which may

contain heuristics or methods tor multi objective decision making (meyerink et al., 1993).

Potential of remote sensing in water management

Remote sensing can be used in various activity domains of the water manager, i.e.

• Surveying and mapping

• Spatial analysis and prediction or forecasting and decision making in real-time. e.g. flood control,

irrigation.



• Surveying and mapping

Is basic to effective water management topographic maps have long been made by photogrammetry using

stereo models of aerial photographs. Basic principles of photogrammetry can be found in lillesand and

kieffer (1994). Topographic base maps are usually available, but map updating is often required nowadays.

new technological developments make it possible to carry out map updating more efficiently than used to be

the case. geometric correction programmes for satellite imagery are a standard procedure in rs packages.

Hence updating of terrain features which are liable to change, such as land cover, river courses, reservoirs,

irrigation areas and so on, can be merged with the topographic base. in addition, some RS/GIS packages

offer the possibility of preparing digital orthophotos of both satellite images and digitally scanned aerial

photographs. this is of particular importance in land and water management, because for large parts of the

world, a land use and tenure or cadastral data base does not exist, or is difficult to access. By image

processing, e.g., edge enhancement filters and multi spectral classifications, at least parceled areas can be

differentiated. The products derived have to be metrically as accurate as possible with corrected height

displacements.

Spatial analysis and regionalization

Remote sensing also makes it possible to prepare a quantitative analysis of water balance components at a

wider range of scales ranging from poor water distribution problems in irrigational areas to delineations of

main hydrological terrain units which may be termed as hydrotopes. Conceptually these hydrological units

are typical sets of hydrological responses. an essential characteristic of hydrological terrain units is that their

boundaries cam to many cases be deduced from remotely sensed imagery, using a pragmatic, open-ended

classification scheme. Knowledge of the effects of terrain factors on the hydrology should assist in

formulation of criteria for their delineation. without analytical image interpretation, the hydrological terrain

units can, to a certain extent, be compiled in a GIS environment by combining a digital geologic map,

topographic derivatives (e.g., slopes), hydrological features (e.g., drainage, lakes, wetlands) and a vegetation

cover classification.



Monitoring and forecasting

The prognosis and monitoring of hydrologic phenomena by remote sensing dually rely on the use of image

time series or multi temporal images from a same area. The idea is to find an empirical correlation between

features measured on imagery & ground hydrometric data. if the two are correlated, the relationship can be

used reduce hydrometric ground operations, usually difficult or expensive, or to fill in the record. Obvious

applications are evaporation estimations from season variable swamp areas, or prediction of snowmelt runoff

from snow cover.

River basins planning with the aid of remote sensing

Development in most countries and regions of the world stands in direct relative to their relation and mastery

of management of water resources. Rational water management should be based upon thorough

understanding; of water availability and movement. the river basin being the physical hydrologic unit, to

which die basic principle of conservation of mass and energy apply is a common and widely adopted concept

m hydrology for assessing water and energy balance components. the water balance is a basic tool for

analyzing the availability of water resources at national, regional or local scale, GIS has proven an excellent

tool to support large scale resource and demands allowing easy aggregation overlaying and querying

between resources and demands (keser & bogardu 1993), since spatial data is needed the mapping potential

of remotely sensed imagery contributes to identification and assessment of component of die water balance

over large areas, furthermore, features can be studied of areas which will benefit from allocated water.

Besides water balance studies, remote sensing has another potential for water management in large river

basins. Full scenes of high resolution imagery of e.g., LANDSAT I or spot can provide synoptic over views

of basics and permit visual or digital interpretation and identification of landscape units, geologic features,

land cover complexes* drainage patterns and geomorphology of floodplains all essential information layers

for solving water management problems.

Hydrologic monitoring & forecasting

a widely known application illustrating the use of weather satellite system for prediction and forecasting of

rainfall and flood hydrology of large international river basins is the river nile monitoring, forecasting and

simulation project this project makes use of the low spatial resolution but high tempore) resolution imagery

weather satellites (MCTCOSAT* NOAA) which are merged with ground data in order to produce spatial



rainfall estimates. These predictions are then used as in water balance and real-time flood routing and

forecasting model of the nile river .

Upstream-downstream interrelationships in river basins

For river basin planning and management, basic knowledge on the upstream-downstream interrelationships is

required hydrologic responses between headwater central basin area and the floodplain delta or estuaries are

unique in every basin and their knowledge is essential for downstream long-term water use, distribution and

planning. transport and delivery of sediment from catchments are important for both (jownstream and within-

basin considerations. relationships between the magnitude 0f sediment yield of basins and climatic,

physiographic and land use controls have been investigated by many researchers (hadley et al., 1985).

knowledge of the distribution of sediment sources and sinks within a basin is essential for recommending

control measures. in general, upstream areas and watersheds may be subject to important man-induced land

use changes or conversions (e.g., deforestation), which might affect downstream hydrology. occurrence of

natural phenomena such as fast geologic erosion processes (i.e., mass wasting), volcanic or seismic activities

can also influence the hydrologic behavior of river basins to a certain extent.

An example from sulawesi (verstappen, 1977), illustrates the use of remote sensing, i.e., stereo aerial

photography, for detecting changes in a river regime of a tropical catchment. The deforestation in the

catchment of the river, shown in fig. has led to an important change in the river morphology which changed

from a meandering river (note the remnants on the floodplain) to a braiding river (the present one). The

wavelength, the width and the gradient all have increased; the sinuosity, the radius of curvature and the

meander amplitude have decreased. The cause of the changes is the sharp increase in the sediment load of the

river. the width to depth ratio has increased and also in absolute terms the depth of the river may be less than

during the former meandering state. attenuation of the peak flows by overbank flow still take place and it is

therefore difficult to conclude whether the peak flows have increased or not. However, the higher discharges

may have become more irregular. The image provides a diagnosis for profound changes in the regime of the

river during recent times.



Example



Watershed management with the aid of remote sensing

Watershed management contains all activities concerning sustained use, protection or rehabilitation of the

water, soil and vegetation resource base in the upper parts or headwater systems of larger river basins.

Various operational levels can be distinguished in watershed management, ranging from large basins,

watersheds, sub-

watershed to local scale (sheng, 1990). As the detail of survey increases, one finally arrives at the farm or

community level of survey and inventory. The range of levels is reflected by the range of spatial resolutions

of aerospace images used. Compared to aerial photographs, satellite images such as LANDSAT MSS, TM

and IRS LISS II, have a relative low spatial resolution. They provide overviews at regional scale, particularly

of land cover. With other information they are used for zoning of areas or watersheds within larger

catchments in order to list priority for treatment. In some countries, the concept of 'critical' areas is used and

the priority depends on the

proportion of critical areas within the catchment. critical areas are those where the land cover which offers

little protection to erosion, such as row crops or overgrazed rangelands, occurring in combination with

certain lithologies — i.e. those where soils] which are susceptible to erosion —, and with dissected, sloping

lands. At the other end of the range, large scale aerial photographs, say, 1:10.000 or 1:20.000 are used. Apart

from the details of land cover and infrastructure visible on the photographs,] they offer the possibility of

stereographic interpretation of the geomorphology and morphometry of the terrain. The topographic

information at large scales thus derived can save much time and costs for the preparation of so called

"engineering designs" for the planning of soil conservation measures which follows the priority assessment

using smaller scales.

Hydrologic photo-interpretation for watershed management

Watershed management, and especially the planning of sustainable soil & water use, requires detailed

hydrologic information pertaining to the terrain and vegetation, as well as to their interactions. The larger

scales of stereo aerial photography are eminently suitable for studying the interactions by visual

interpretation. These interpretations must be embedded in basic background knowledge of geology,

geomorphology and soils and on the effects of such terrain factors on the hydrology of the area.



Small-scale water resource development and remote sensing

It can be generally expected that the attention to small-scale water resource develop-ment will continue to

increase in the near future, considering the environmental problems and world-wide debate about large dams

(siwt, 1994). also the excessive exploitation and contamination problems of large groundwater aquifers in

several countries (vbra & zaporozec, 1994), the water quality impacts of agriculture, urbanization and

industry on surface waters in general lead to an increased stress per capita on drinking water availability on a

worldwide basis. Zoning and design of local water development schemes in a certain region require the study

of the enormous variation of combinations of terrain and vegetation factors in nature.

Without the use of remotely sensed imagery, it is difficult to avail of sufficient information, considering the

lack of soil maps and hydrometric information in large parts of the world. The following two paragraphs

illustrate the use of remote sensing in some typical small-scale water resource development operations.

Flood spreading and groundwater recharge

The following example illustrates the use of remote sensed imagery for locating a flood-spreading scheme

for shallow groundwater recharge, to be used for local irrigation. Colour Plate 15.B shows a color composite

image of Landsat 5 Thematic Mapper bands 4, 7 and 1 of a study area east of Fasa, Shiraz, Southern Iran.

Episodic flood runoff in this region is lost to playas or to the sea. Some of that water can be intercepted using

a floodwater spreading scheme for artificial recharge, if three criteria are satisfied: (a) the catchment must

have an adequate size to generate sufficient runoff, but not be too large to deal with high discharges for a

simple diversion, (b) the area of infiltration should be close to the ephemeral river and be underlain by

permeable deposits, and (c) the infiltrated water should recharge a shallow aquifer from which the water can

be pumped for irrigation. As can be seen on the image, the criteria are met in this case. Peak flows from the

moderately sized catchment (shown in part) are diverted from the river where it flows on an alluvial fan (A),

into parallel diversion channels which feed - sandy - infiltration basins (B), described in detail by Kowsar

(1989). The evidence of an aquifer can be inferred from the presence of groundwater irrigated fields at the

lower part of the alluvial fan. Geomorphological interpretation of the image leads to a differentiation of

deposits of small local fans (D), not of interest, the upper sandy part of the main alluvial fan (A) Sutable for a

recharge scheme, and the lower part (C) with heavier soil textures. The latter part may be less suitable for



artificial infiltration, but has fewer losses of irrigation water. A ground water model was used to assessment of recharge.

Runoff water harvesting with the aid of remote sensing

Runoff water harvesting basically is a technique by which surface runoff is collected purposely in a smaller

infiltration area, where it can be used for crop production or plant growth. The technique of collecting

rainwater was already practiced during early civilisations (hillel, 1967). The determination of potential sites

for runoff harvesting or irrigation require besides knowledge of the rainfall regime characteristics, a detailed



evaluation of surface topography, surface soil properties and other site environmental parameters. Remote

sensing techniques combined with geography information systems have been applied to screen larger areas

for potential runoff irrigation sites in the sahelian region (tauer & humborg, 1992). For more detailed

surveys, large scale stereo-images enable the identification and mapping of some of the relevant parameters.

Irrigation water management and remote sensing

It is estimated that the world's irrigated area is at present in the order of 270 milium ha. this is only 17% of

the world's total cropped area but accounts for about one third of the world's food harvest (smedema, 1993).

despite this important contribution to agriculture, the performance of the irrigated agriculture sector has, in

general, been disappointing. a basic reason is the low efficiency in the use of available water resources. In

some projects, 60% of the diverted water does not actually contribute to crop water requirements. technical

problem, arise because irrigation water supplies have not been well been distributed. at the form level, water

supply may be unreliable supply and demands seem rarely to coincide or farmers practice poor and

inefficient irrigation methods.

Remote sensing technique permit the quantitative analysis of problems associated with the poor water

distribution of irrigation perimeters .Inadequate water supply is clearly reflected in differences in cropping

patterns intensities and crop development features which can be conveniently detected and mapped by

satellite images.

The remote sensing when was introduced in hydrology in seventies held a great deal if promise for hydrology

in spite of promise applied over engineering hydrology has bee slow to embrace remote sensing as a useful

recourse of data presumably because existing techniques and data has been satisfactory for limited

applications although the remote sensing is going to be proved great for hydrology and water resources

• Conclusion

• The ability to provide spatial data, rather than point data.

• The potential to provide measurement of hydrological variables not available through traditional techniques

such as soil moisture and snow water content.



• The ability, through satellite sensors, to provide long-term, global-wide even for remote and generally

inaccessible regions of the earth,

• The possibility, to acquire rs data for larger areas with a high resolution in space and time at one spot (e.g.

weather radar receiving station, satellite center) and in real-time, which may serve as basis for water

management decision in real-time.

OUR VISION

[Type text]

BIBILOGRAPHY

1)REMOTE SENSING IN HYDROLOGY AND WATER MANAGEMENT :SCHULTZ AND

ENGMAN

2)APPLICATIONS OF REMOTE SENSING TO HYDROLOGY AND HYDROGEOLOGY :

MARWAN KOUDMANI

remote sensing in hydrology

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