HJ-1A HSI on-orbit radiometric calibration and validation research

The calibration experiment data at Dunhuang radiometric calibration site in October, 2008 were used to achieve the on-orbit radiometric calibration for HJ-1A hyper spectral imager (HSI). Two other field experiments data were used to validate the Dunhuang calibration results. One field experiment took place in Inner-Mongolia, China in September, 2008, and the other field experiment took place in Lake Frome, Australia in February, 2009. Finally, the ‘confidence interval of calibration error’ concept was put forward for quantitatively computing the calibration coefficient error confidence interval. The results showed that the Dunhuang calibration results in 2008 had high reliability. The confidence intervals of calibration error for all HSI channels were between 2% to 12%, which could satisfy the requirement of the HSI quantitative applications.

VICARIOUS RADIOMETRIC CALIBRATION OF SATELLITE FY-ID SENSORS AT VISIBLE AND NEAR INFRARED CHANNELS

For the problem of in-flight test site radiometric calibration for the FY-1D Meteorological Satellite onboard sensor's visible and near infrared channels,this paper described the calibration method,satellite-ground synchronous observation data acquired at China Dunhuang Calibration Test Site,parameter derivation and radiative transfer computation during the calibration,and the calibration result analysis.At FY-1D seven channels (with central wavelength at Channels 1:630 nm,2:865 nm;6:1610 nm;7:455 nm,8:505 nm;9:555 nm;10:932 nm),calibration coefficients obtained during the ground site calibration were compared with that respectively of pre- launch calibration.It is demonstrated that results of FY-1D onboard two sensors' (A and B) at channels 1,2,6 and 10 were close to pre-calibration,and the absolute difference of Gobi desert reflectance computed using test site and pre-launch calibration coefficients was no more than 2%. At other channels,large pre-launch calibration errors resulted in a poor consistency between the test site and pre-launch calibration.The errors can be corrected by the test site calibration results. Based on a rough estimation,the overall error of the calibration was about 6%. The paper also presented the in-flight vicarious calibration at the visible and near infrared channels of FY-1C sensor A which was launched in 1999 and has been put into operational mode since 2002.The results exhibit that FY-1C sensor's response has 23% attenuation at Channels 7 and 8,while only minor degradation at the other channels was found. During the mission,calibrations were also conducted at NOAA-17's Channels 1 and 2 (1:430 -830 nm,2:500--1072 nm).A very good consistency has been achieved between the test site and pre-launched calibration results.

Terrain radiometric calibration of airborne UAVSAR for forested area

In the field of biomass estimation,terrain radiometric calibration of airborne polarimetric SAR data for forested areas is an urgent problem.Illuminated area correction ofσ-naught could not completely remove terrain features.Inspired by Small and Shimada,this paper tested gamma-naught on one mountainous forested area using airborne Uninhabited Aerial Vehicle Synthetic Aperture Radar data and found it could remove most terrain features.However,a systematic increasing trend from far range to near range is found in airborne SAR cases.This paper made an attempt to use the relationship between distance to SAR sensor andγ-naught to calibrateγ-naught.Two quantitative evaluation methods are proposed.Experimental results demonstrate that variation ofγ-naught can be constrained to a limited extent from near range to far range.Since this method is based on ground range images,it avoids complicated orthorectification.

Estimation of Thermal Imaging System Operating Range Based on Background Radiation

Traditional operating range prediction methods assume that the atmospheric radiances in a target path and a background path are equal. But they are different in a real-world environment. To solve this problem,the influence of atmospheric radiance on operating range prediction is analyzed in this paper. Range estimation model in thermal imaging based on background radiation（ REBR） is proposed. Infrared image radiometric calibration is used to calculate the background radiation of a system entrance pupil. The result shows that,compared with traditional operating range prediction methods,the REBR method is more suitable for the actual atmospheric transmission process and the physical process of infrared imaging.

An unmanned ground vehicle phenotyping-based method to generate three-dimensional multispectral point clouds for deciphering spatial heterogeneity in plant traits

Fusing three-dimensional(3D)and multispectral(MS)imaging data holds promise for high-throughput and comprehensive plant phenotyping to decipher genome-to-phenome knowledge.Acquiring high-quality 3D MS point clouds(3DMPCs)of plants remains challenging because of poor 3D data quality and limited radiometric calibration methods for plants with a complex canopy structure.Here,we present a novel 3D spatial–spectral data fusion approach to collect high-quality 3DMPCs of plants by integrating the next-best-view planning for adaptive data acquisition and neural reference field(NeREF)for radiometric calibration.This approach was used to acquire 3DMPCs of perilla,tomato,and rapeseed plants with diverse plant architecture and leaf morphological features evaluated by the accuracy of chlorophyll content and equivalent water thickness(EWT)estimation.The results showed that the completeness of plant point clouds collected by this approach was improved by an average of 23.6%compared with the fixed viewpoints alone.The NeREF-based radiometric calibration with the hemispherical reference outperformed the conventional calibration method by reducing the root mean square error(RMSE)of 58.93%for extracted reflectance spectra.The RMSE for chlorophyll content and EWT predictions decreased by 21.25%and 14.13%using partial least squares regression with the generated 3DMPCs.Collectively,our study provides an effective and efficient way to collect high-quality 3DMPCs of plants under natural light conditions,which improves the accuracy and comprehensiveness of phenotyping plant morphological and physiological traits,and thus will facilitate plant biology and genetic studies as well as crop breeding.

Challenges to quantitative applications of Landsat observations for the urban thermal environment

Since the launch of its first satellite in 1972, the Landsat program has operated continuously for more than forty years. A large data archive collected by the Landsat program significantly benefits both the academic community and society. Thermal imagery from Landsat sensors, provided with relatively high spatial resolution, is suitable for monitoring urban thermal environment. Growing use of Landsat data in monitoring urban thermal environment is demonstrated by increasing publications on this subject, especially over the last decade. Urban thermal environment is usually delineated by land surface temperature（LST）. However, the quantitative and accurate estimation of LST from Landsat data is still a challenge, especially for urban areas. This paper will discuss the main challenges for urban LST retrieval, including urban surface emissivity, atmospheric correction, radiometric calibration, and validation. In addition, we will discuss general challenges confronting the continuity of quantitative applications of Landsat observations. These challenges arise mainly from the scan line corrector failure of the Landsat 7 ETM ＋ and channel differences among sensors. Based on these investigations, the concerns are to：（1） show general users the limitation and possible uncertainty of the retrieved urban LST from the single thermal channel of Landsat sensors;（2） emphasize efforts which should be done for the quantitative applications of Landsat data; and（3） understand the potential challenges for the continuity of Landsat observation（i.e., thermal infrared） for global change monitoring, while several climate data record programs being in progress.