Validation Of Remote Sensing Products Research Articles

Structure design and implementation of a high stability semi-submersible optical buoy for marine environment observation

Marine optical buoys are recognized as highly effective technical means for obtaining long-term continuous ocean optical observation data for on-orbit ocean color satellite radiometric calibration and remote sensing product validation. The high stability of a buoy's body structure is a crucial factor for marine optical buoys to operate in complex environments, such as in the presence of wind, waves, and currents. In this study, we propose a highly stable self-counterweight transverse-tethered semi-submersible buoy structure achieved through buoy structure design, mooring system design, mechanical analysis and numerical simulation analysis, and transverse-tethered point analysis. The novel buoy design underwent a marine environment adaptability test, demonstrating an improved ability to resist wind and waves while also greatly reducing the difficulty and cost of design and deployment. In-situ verification showed that the buoy's swing angle was better than ±10° under a 3–4 level sea state, meeting marine optical buoy requirements and proving the new buoy design suitable for harsh and complex marine conditions.

Indirect Measurement of Forest Canopy Temperature by Handheld Thermal Infrared Imager through Upward Observation

The influence of leaf temperature on transpiration, photosynthesis, respiration, and other metabolic activities is critical to plant growth, development, production and distribution. However, traditional measurement of canopy temperature by thermocouples or thermal infrared thermometers is laborious and difficult, especially for tall trees. The recent development of a handheld thermal infrared imager has made it possible to perform high temporal and spatial canopy temperature measurements efficiently. However, the signal recorded by the sensor is often a mixture of radiation from the target and the atmosphere, which must be corrected to get the true temperature. In this study, we propose a ground-based indirect measurement method of canopy temperature by a handheld thermal infrared imager through upward observation. Visible and thermal images are combined to distinguish the canopy pixels and sky pixels. To remove the atmospheric radiation from the sky, an empirical atmospheric model is established, which can perform atmospheric correction accurately and efficiently. To validate the proposed method, we collected canopy temperatures of 36 species of trees with a FLIR T420 thermal infrared imager and compared the estimated temperatures with those directly measured by thermocouples. The accuracy of the corrected canopy temperature has been significantly improved with mean absolute error reduced from 3.73 °C to 0.64 °C. This proposed canopy temperature measurement method can be used to various applications in remote sensing product validation, and ecosystem and forestry studies.

A comprehensive dataset of vegetation states, fluxes of matter and energy, weather, agricultural management, and soil properties from intensively monitored crop sites in western Germany

Abstract. The development and validation of hydroecological land-surface models to simulate agricultural areas require extensive data on weather, soil properties, agricultural management, and vegetation states and fluxes. However, these comprehensive data are rarely available since measurement, quality control, documentation, and compilation of the different data types are costly in terms of time and money. Here, we present a comprehensive dataset, which was collected at four agricultural sites within the Rur catchment in western Germany in the framework of the Transregional Collaborative Research Centre 32 (TR32) “Patterns in Soil–Vegetation–Atmosphere Systems: Monitoring, Modeling and Data Assimilation”. Vegetation-related data comprise fresh and dry biomass (green and brown, predominantly per organ), plant height, green and brown leaf area index, phenological development state, nitrogen and carbon content (overall > 17 000 entries), and masses of harvest residues and regrowth of vegetation after harvest or before planting of the main crop (> 250 entries). Vegetation data including LAI were collected in frequencies of 1 to 3 weeks in the years 2015 until 2017, mostly during overflights of the Sentinel 1 and Radarsat 2 satellites. In addition, fluxes of carbon, energy, and water (> 180 000 half-hourly records) measured using the eddy covariance technique are included. Three flux time series have simultaneous data from two different heights. Data on agricultural management include sowing and harvest dates as well as information on cultivation, fertilization, and agrochemicals (27 management periods). The dataset also includes gap-filled weather data (> 200 000 hourly records) and soil parameters (particle size distributions, carbon and nitrogen content; > 800 records). These data can also be useful for development and validation of remote-sensing products. The dataset is hosted at the TR32 database (https://www.tr32db.uni-koeln.de/data.php?dataID=1889, last access: 29 September 2020) and has the DOI https://doi.org/10.5880/TR32DB.39 (Reichenau et al., 2020).

Understanding the Heterogeneity of Soil Moisture and Evapotranspiration Using Multiscale Observations From Satellites, Airborne Sensors, and a Ground-Based Observation Matrix

This letter summarizes a special stream of the IEEE Geoscience and Remote Sensing Letters devoted to understanding the heterogeneity in soil moisture, evapotranspiration, and other related ecohydrological variables based on multiscale observations from satellite-based and airborne remote sensors, a flux observation matrix, and an ecohydrological wireless sensor network in the Heihe Watershed Allied Telemetry Experimental Research project. Scaling and uncertainty are the key issues in the remote-sensing research community, especially regarding the heterogeneous land surface. However, a lack of understanding and an inadequate theoretical basis impede the development and innovation of forward radiative transfer models, as well as the quantitative retrieval and validation of remote-sensing products. We summarize the prior considerations regarding surface heterogeneity research and report the main outcomes and contributions of this special stream. The highlights of this stream are related to spatial sampling, upscaling, uncertainty analysis, the validation of remote-sensing products, and accounting for heterogeneity in remote-sensing models.

COMPREHENSIVE CALIBRATION AND VALIDATION SITE FOR INFORMATION REMOTE SENSING

Abstract. As a naturally part of information technology, Remote Sensing (RS) is strongly required to provide very precise and accurate information product to serve industry, academy and the public at this information economic era. To meet the needs of high quality RS product, building a fully functional and advanced calibration system, including measuring instruments, measuring approaches and target site become extremely important. Supported by MOST of China via national plan, great progress has been made to construct a comprehensive calibration and validation (Cal&Val) site, which integrates most functions of RS sensor aviation testing, EO satellite on-orbit caration and performance assessment and RS product validation at this site located in Baotou, 600km west of Beijing. The site is equipped with various artificial standard targets, including portable and permanent targets, which supports for long-term calibration and validation. A number of fine-designed ground measuring instruments and airborne standard sensors are developed for realizing high-accuracy stepwise validation, an approach in avoiding or reducing uncertainties caused from nonsynchronized measurement. As part of contribution to worldwide Cal&Val study coordinated by CEOS-WGCV, Baotou site is offering its support to Radiometric Calibration Network of Automated Instruments (RadCalNet), with an aim of providing demonstrated global standard automated radiometric calibration service in cooperation with ESA, NASA, CNES and NPL. Furthermore, several Cal&Val campaigns have been performed during the past years to calibrate and validate the spaceborne/airborne optical and SAR sensors, and the results of some typical demonstration are discussed in this study.

A Prototype Network for Remote Sensing Validation in China

Validation is an essential and important step before the application of remote sensing products. This paper introduces a prototype of the validation network for remote sensing products in China (VRPC). The VRPC aims to improve remote sensing products at a regional scale in China. These improvements will enhance the applicability of the key remote sensing products in understanding and interpretation of typical land surface processes in China. The framework of the VRPC is introduced first, including its four basic components. Then, the basic selection principles of the observation sites are described, and the principles for the validation of the remote sensing products are established. The VRPC will be realized in stages. In the first stage, four stations that have improved remote sensing observation facilities have been incorporated according to the selection principles. Certain core observation sites have been constructed at these stations. Next the Heihe Station is introduced in detail as an example. The three levels of observation (the research base, pixel-scale validation sites, and regional coverage) adopted by the Heihe Station are carefully explained. The pixel-scale validation sites with nested multi-scale observation systems in this station are the most unique feature, and these sites aim to solve some key scientific problems associated with remote sensing product validation (e.g., the scale effect and scale transformation). Multi-year of in situ measurements will ensure the high accuracy and inter-annual validity of the land products, which will provide dynamic regional monitoring and simulation capabilities in China. The observation sites of the VRPC are open, with the goal of increasing cooperation and exchange with global programs.

TECHNICAL SPECIFICATION FOR THE VALIDATION OF REMOTE SENSING PRODUCTS

Abstract. The validation of remote sensing products (RSPs) is fundamental work before the proper use of RSPs. This paper mainly introduces the technical specification for the validation of remote sensing product, which is used to guide user how to validate the available products. The validation of remote sensing products (VRSP) mainly there are two levels. The first level focuses on the validation at pixel scale and the other is the product level which contains a number of pixels that are distributed in different land use types which are selected to represent both the space-time characteristics of surface parameters investigated. At pixel scale, the validation procedure mainly consists of three steps: sampling design for ground observation, data collection and estimation the mean value at pixel scale. The data types of ground observation include the wireless sensor network, which are used to capture multi-scale heterogeneities of surface parameters, and the footprint which could be a flux observation such as eddy covariance (EC) and large aperture scintillometer (LAS). After finishing the validation at pixel scale, the second-level validation for the whole remote sensing product is followed. The assessment with indexes is then used to evaluate the performance of the validation. Last, a validation report on the description of the validation will be included in the technical specification.

RESEARCH ADVANCES ON RADIATION TRANSFER MODELING AND INVERSION FOR MULTI-SCALE LAND SURFACE REMOTE SENSING

Abstract. At first, research advances on radiation transfer modeling on multi-scale remote sensing data are presented: after a general overview of remote sensing radiation transfer modeling, several recent research advances are presented, including leaf spectrum model (dPROS-PECT), vegetation canopy BRDF models, directional thermal infrared emission models(TRGM, SLEC), rugged mountains area radiation models, and kernel driven models etc. Then, new methodologies on land surface parameters inversion based on multi-source remote sensing data are proposed. The land surface Albedo, leaf area index, temperature/emissivity, and surface net radiation etc. are taken as examples. A new synthetic land surface parameter quantitative remote sensing product generation system is designed and the software system prototype will be demonstrated. At last, multi-scale field experiment campaigns, such as the field campaigns in Gansu and Beijing, China will be introduced briefly. The ground based, tower based, and airborne multi-angular measurement system have been built to measure the directional reflectance, emission and scattering characteristics from visible, near infrared, thermal infrared and microwave bands for model validation and calibration. The remote sensing pixel scale "true value" measurement strategy have been designed to gain the ground "true value" of LST, ALBEDO, LAI, soil moisture and ET etc. at 1–km2 for remote sensing product validation.

Prior knowledge-based retrieval and validation of information from remote-sensing data at various scales

This is the preface to the special issue on the use of prior knowledge for quantitative remote sensing and validation of results from quantitative remote sensing at different spatial scales. Quantitative remote sensing is the inverse problem of retrieval of geophysical and biophysical parameters using remote-sensing data. This is usually a non-linear ill-posed problem. To overcome the ill-posed problems of retrieval, prior knowledge is normally used. Validation is a general scientific issue for the remote-sensing community. Frequent validation of remote-sensing products is necessary to ensure their quality and accuracy. This special issue includes articles on in situ measurements from a field campaign, the accuracy and precision of calibration, validation methods, and evaluation of remote-sensing quantitative retrieval information modelling. Because of the insufficient study of the validation of quantitative remote-sensing products and the lack of validation theories and practical methods, in particular, a scaling theory for heterogeneous land surface variables, further applications of remote-sensing data and products are limited.