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Polarimetric Measurements of Snow, Soil and Vegetation


Polarimetric, Active-Passive, Combined Measurements of Snow, Bare Soil, Wheat and Herbaceous Vegetation at L-, C-, and X-band Frequencies

Tech Area / Field

  • ENV-MIN/Monitoring and Instrumentation/Environment
  • ENV-WPC/Water Pollution and Control/Environment
  • PHY-RAW/Radiofrequency Waves/Physics

8 Project completed

Registration date

Completion date

Senior Project Manager
Rudneva V Ya

Leading Institute
Institute of Radiophysics and Electronics, Armenia, Ashtarak-2

Supporting institutes

  • ECOSERV Remote Observation Centre Co. Ltd., Armenia, Yerevan


  • Forschungszentrum Karlsruhe Technik und Umwelt / Institute of Meteorology and Climate Research, Germany, Karlsruhe\nDeutsches Zentrum für Luft- und Raumfahrt e.V. / Institute of Radio Frequency Technology and Radar Systems, Germany, Wessling\nFriedrich-Wilhelms-Universitat Bonn / Meteorologisches Institut, Germany, Bonn

Project summary

The main objectives of the Project are:

To perform a series of polarimetric, spatial-temporal combined active (bistatic) – passive measurements on pasture and wheat fields at L-, C-, and X-band frequencies over a wide range of incidence angles. To study the feasibility of soil and land snow cover moistures retrieval from combining radar and radiometer data acquiring from snow and bare soils, and from surfaces covered with short, dense, and herbaceous vegetation and wheat. To develop new methods and algorithms for soil and snow moistures retrieval, and for soil vegetation classification, from combining data of polarimetric, multi-frequency radar-radiometer observations. To develop the structure of corresponding radar-radiometer system for airborne or ground transportable utilization.

Technical approach:

Determining the water content in soil and snow is essential to many application in meteorology, agriculture, hydrology, environmental security and protection, civil engineering, and building. A weight related definition (dry or wet) is preferred in soil mechanics and civil engineering. Hydrologists, on the other hand, require volume related water content for evaluating transport equation. For agriculture, if a simple method can be refined to simultaneously detect nitrogen (fertilizer) and moisture stress, farmers would readily adopt a new technology to optimize the quality and quantity of the wheat harvest, for instance. Environmental benefits would include less ground water pollution or offsite contamination, as well as decreased energy, nutrient, and irrigation inputs. In the building material industry the level of air pore saturation is the requested quantity. Most of the measuring techniques known to date are unable, however, to meet requirements of accuracy, reproducibility, expense of time and labor, as well as automation capability.

High frequency measurements are known to be most suitable because of the special dielectric properties of water. The dielectric method is an indirect way to measure the soil water content. And, for instance, the method of measurement and evaluation in the frequency and time domain by high frequency cables buried into the soil or enclosed by snowfall allow both the integral water content and the locally resolved moisture distribution along the cable to be determined. Such methods and techniques has mostly scientific application to research high frequency or microwave dielectric properties of the soil and snow packs, for understanding of the measurement principles and for development of new sensors and methods which could cover large area of survey. In this aspect, microwave active and passive remote sensing methods and sensors currently have wide application in the soil and snow covers survey. Each of them has its own advantage and shortage. Particularly, high spatial resolution of current space borne radars allow to carry out detail survey of an area such as a farmer's field and evaluate soil moisture and snow water content of the observed surface. However, radar methods do not permit yet to distinguish, for sample, dry snow from bare soil, as well as some vegetation and surface roughness properties. Microwave passive methods provide poor spatial resolution from the space (regarding to radar methods) but could be more applicable for soil moisture and snow cover parameters aerial (airborne) evaluation due to its easy multi-frequency application and low energetic requirements. Despite the mentioned advantages both radar and radiometric methods suffer from multi-parameter dependencies of the snow and soil surface radar cross sections and their brightness temperature, which limit the accuracy of the soil and snow moistures retrieval. Really, it is known that the soil surface radar backscattering coefficient and its brightness temperature are complicated functions of various principal parameters, namely; soil moisture, soil sort and structure, surface roughness, snow and vegetation parameters, underground water levels, etc, and some of them have comparable influence on the changes of the soil surface radar backscattering coefficient and its brightness temperature absolute values.

For an unambiguous and accurate retrieval of snow and soil moistures and classification of soil vegetation a wider set of independent measurements and a synergy of various sensors are required. Since, microwave signals backscattered from and emitted by the land snow cover, the bare soil surface and the soil vegetation may be considered as independent variables, the synergetic application of microwave radar and radiometer observations for soil and snow moistures retrieval represents special interests. For its successful implementation it is important and actual to perform multi-frequency, polarimetric, microwave, active-passive combined measurements of snow, bare soil and soil vegetation, and on the basis of acquired data to develop new methods and algorithms providing the possibility to reach high precision in snow and soil moistures retrieval and in soil vegetation classification. Proposed tasks' solution is important and topical for current and future land microwave remote sensing programs based on a variety of imaging sensors, which will provide timely and iterative multi-sensor observation data on a global scale. This project on land (snow, soil and vegetation) microwave remote sensing will benefit national studies in many ways, and will present wide interest for Armenian, Former Soviet Union (FSU) and Foreign inpidual research institutions, companies and space agencies. It is expected that the results from this study will benefit those experimentalist and industries which require knowledge of the location of underground water horizons (levels), soil, vegetation and snow covers features.

Anticipated results:

The main research results and achievements are expected to be:

– Methodology for combining data of land radar-radiometer observations.

– Method development for snow and soil moistures precise retrieval.
– Classification possibilities of observed surface vegetation.
– Improvement of snow, soil and soil vegetation parameters retrieval's precision.
– Development of a structure of multi-frequency, polarimetric, combined radar-radiometer system for airborne or ground transportable utilization for snow, soil and soil vegetation parameters real time and precise retrievals.

The results of suggested investigations could provide new quality in land surface (soil) remote sensing and environmental monitoring. They will allow:

– Derive a technique for synergy of data of land surface radar-radiometer observation.

– Study microwave reflective-emissive joint features of the snow, bared soil and soil vegetation.
– Derive new parameters and criteria for real time retrieval of snow and soil moistures and vegetation parameters.

The results of these investigations have significant commercial value, particularly in hydrology, in agriculture and in irrigation. Aerial radar-radio thermal images of observed areas, such as a farmer's fields can be used in farming to detect a lack of water and fertilizer, for defining and mapping underground water horizons, as well as for underground water reservoirs and hazardous waste sites detection and identification in completion with ultra low frequency electromagnetic geophysical systems requiring additional information about upper layer conductivity. Aerial utilization of microwave methods and devices for soil and snow moistures retrieval, and soil vegetation and hazardous waste areas investigations and data processing will cost about 0.1-0.2 USD per acre.

For this research project implementation Armenian and foreign research teams’ collaboration is essential. There are some reasons for that:

– Manufacturing of high stable and sensitive L-, C-, and X-band noisy transmitters and radiometers, supplied by antennas.

– Calibration and field trials problems of manufactured microwave devices.
– Difficulties of experimental and theoretical tasks solution related with snow, soil and soil vegetation microwave, polarimetric, reflective and emissive characteristics measurements.
– Large capacity of supposed measurements, data processing and analysis.
– Cultivating problems of the test areas under wheat crop and herbaceous vegetation.
– New methods and algorithms development necessity.
– Methodological and technical complexities of experimental data processing.
– Administrative and organization tasks, reports’ drawing, etc.

The following participating-organizations and foreign collaborators will be involved in this project’s implementation activities, namely:

Institute of Radiophysics and Electronics (IRPhE) of Armenian National Academy of Sciences (ANAS) during last 35 years was one of the leading organizations in the USSR in the field of development of high-sensitivity radiometers, polarimeters, phasemeters, high-power oscillators and other microwave and near-IR devices. The unique equipment was designed exclusively for classified military purposes, as well as far-distance space communication sites. Regular parameter measurements of large antenna systems, using space radio sources, were performed only by the IRPhE specialists and by their developed equipment. Theoretical and experimental researches and developments, having the aim to create highly sensitive MW and IR receivers and differential phase and amplitude meters of electromagnetic field are the essential part of the IRPhE activities. Multi-year experience of personnel, as well as the existing unique instruments and equipment may be successfully redirected to civil purposes. The proposed Project will efficiently use this research and technological potential.

ECOSERV Remote Observation Centre (ROC) Co.Ltd. has gathered together former defense (weapon) scientists, engineers and technicians to redirect their scientific and technical knowledge for civil purposes, particularly for sustainable monitoring, security and protection of the Environment. Multi-year experience of its personnel in development and manufacturing of various radio systems (radars, scatterometers, microwave radiometers, SAR) for defense purposes (targets detection, identification, navigation and tracking), in manufactured devices field trial and calibration, in field experiments performance and experimental data processing and analysis will undertake the successful implementation of the Project. The ECOSERV ROC will provide test areas, supplied with electricity and water, for calibration and control measurements performance. It will maintain (cultivate, fertilize, water, spray, etc.) the test fields for microwave measurements in appropriate conditions and will perform requiring physical-chemical and biological test measurements and analysis.

ECO-99 Ecological Public Organization (EPO) with the main activities in agriculture and ecology has the aim to improve ecological situation in Armenia by making useless soils suitable for cultivation. The ECO-99 EPO personal are experienced researchers and lecturers, working in the field of agriculture, chemistry and biology in Armenian Agricultural Academy and in various research institution of ANAS. The ECO-99 EPO performs the project “Model Farm” supported by World Council of Churches and the ECLOF. The ECO-99 EPO will put its 20hectare irrigated experimental fields (vegetation and wheat areas, and pastures) and personal at the Project implementation disposal. The ECO-99 EPO will maintain (to cultivate, to fertilize, to water, to spray, etc.) the test fields for microwave measurements in appropriate conditions and to perform requiring chemical and biological tests and analysis.

Project duration is 36 months, starting from its commencement date. The Project includes execution of the following eight Tasks.

– Development and manufacturing of L- (~1.25 GHz), C- (~5.35 GHz), and X- (~9.65 GHz) band active and passive devices (noisy transmitters on the basis of standard noise generators and radiometric receivers).

– Development and manufacturing of transmitting and receiving antennas, and TDR probes (time domain reflectometer) of ~300 MHz and ~900 MHz for in-situ control measurements of soil and snow moistures.

– Laboratory trials of manufactured active and passive devices, antennas, and TDR probes.

– Assembling, calibration and field testing of L-, C-, and X-band active-passive systems and TDR probes.

– Cultivating of the test areas and experimental (farmer’s) fields under wheat crop and herbaceous vegetation.

– L-, C-, and X-band, polarimetric, spatial-temporal collocated, active (bistatic) and passive measurements of the bare soil, snow and soil vegetation of the test areas and farmers' fields.

– Experimental data processing, analysis and comparison with the results of existing theoretical and experimental investigations.

– New methods, algorithms and structures of corresponding systems development for soil and snow moistures retrieval, and for soil vegetation classification.

Active-passive measurements will be conducted for various extreme vegetation conditions, including a bare soil situation (before and after the tillage), the early stage of vegetation growth, in the middle of the season for a fully grown and mature vegetation condition, when vegetation biomass is maximum, and toward the end of the season in stubbly fields and when the leaves will be fallen and the plants will be drier in pasture. For each vegetation condition microwave, active-passive measurements will also be conducted under different soil moisture conditions, to examine the sensitivity of radar backscatter and proper radio thermal emission to soil moisture. Simultaneously with radar-radiometer measurement, a complete set of ground truth data, including the moisture content, size and number density of corns, leaves, stems and pods will also be collocated. The dielectric constant of leaves and steams will be measured immediately after each microwave measurements. Before and after of each set of measurements sky, water surface and absolute black bodies’ brightness temperatures will be recorded. To increase the accuracy of absolute measurements the noise temperatures of external, thermo-stable caliber signals will be recorded too. It is supposed to carry out also simultaneous radar-radiometer measurements of the test areas snow covers reflective and emissive characteristics during winter period. Simultaneously with radar-radiometer measurement, a complete set of snow cover parameters; snowfall depth, snow water content, soil and air temperatures, etc. will also be collocated.

Seven Foreign Collaborators from the USA (3), Germany (3) and Japan, namely: the Environmental Technology Laboratory of the NOAA (ETL/NOAA), the Jet Propulsion Laboratory of California Institute of Technology (JPL), the Morgan State University (MSU), the Center for Northeast Asian Studies, Tohoku University, the Institute of Meteorology and Climate Research (IMCR), Forschungszentrum Karlsruhe, the Institute of Radio Frequency Technology and Radar Systems (IRFTRS) of the German Aerospace Center, Meteorological Institute of the Bonn University (MIBU) have expressed their interest and agreement in collaboration. Participation in the development of project proposal and work plan, joint theoretical and experimental investigations, exchange of information during project implementation, mutual review of technical reports, consultation on Intellectual Property Rights, in case of joint invention, joint discussion of project results, consultations, meetings at conferences and direct visits can be the form of the collaboration.

The project implementation will provide an opportunity for 13 former USSR weapon scientists, were earlier engaged in development of methods and radio systems for targets navigation and tacking, targets detection and identification, to redirect their knowledge and skills to peaceful activities particularly in a field of environmental protection. It will promote integration of scientists of CIS states into the international scientific community, particularly of the USA and Japan. It will contribute to the solution of national and international technical problems applied to the environmental security and protection, hydrology and food program (agriculture and irrigation). Commercial value of anticipated results is high and evidently connects with current requirements to get sustainable information from wide areas of the Earth.

After project completion a stage of development of multi-frequency, polarimetric, combined radar-radiometer system for airborne or ground transportable utilization is planned. For that task solution we intend to use the IRPhE and the ECOSERV ROC research and technological potentials.


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