Intercomparison of In Situ Sensors for Ground-Based Land Surface Temperature Measurements.

Praveena Krishnan,Edward J. Dumas,David Senn,Mark Heuer,Simon J. Hook,Tilden P. Meyers

doi:10.3390/s20185268

Abstract

Land surface temperature (LST) is a key variable in the determination of land surface energy exchange processes from local to global scales. Accurate ground measurements of LST are necessary for a number of applications including validation of satellite LST products or improvement of both climate and numerical weather prediction models. With the objective of assessing the quality of in situ measurements of LST and to evaluate the quantitative uncertainties in the ground-based LST measurements, intensive field experiments were conducted at NOAA’s Air Resources Laboratory (ARL)’s Atmospheric Turbulence and Diffusion Division (ATDD) in Oak Ridge, Tennessee, USA, from October 2015 to January 2016. The results of the comparison of LSTs retrieved by three narrow angle broadband infrared temperature sensors (IRT), hemispherical longwave radiation (LWR) measurements by pyrgeometers, forward looking infrared camera with direct LSTs by multiple thermocouples (TC), and near surface air temperature (AT) are presented here. The brightness temperature (BT) measurements by the IRTs agreed well with a bias of <0.23 °C, and root mean square error (RMSE) of <0.36 °C. The daytime LST(TC) and LST(IRT) showed better agreement (bias = 0.26 °C and RMSE = 0.67 °C) than with LST(LWR) (bias > 1.1 and RMSE > 1.46 °C). In contrast, the difference between nighttime LSTs by IRTs, TCs, and LWR were <0.47 °C, whereas nighttime AT explained >81% of the variance in LST(IRT) with a bias of 2.64 °C and RMSE of 3.6 °C. To evaluate the annual and seasonal differences in LST(IRT), LST(LWR) and AT, the analysis was extended to four grassland sites in the USA. For the annual dataset of LST, the bias between LST (IRT) and LST (LWR) was <0.7 °C, except at the semiarid grassland (1.5 °C), whereas the absolute bias between AT and LST at the four sites were <2 °C. The monthly difference between LST (IRT) and LST (LWR) (or AT) reached up to 2 °C (5 °C), whereas half-hourly differences between LSTs and AT were several degrees in magnitude depending on the site characteristics, time of the day and the season.

Highlights

Land surface temperature (LST), the thermodynamic temperature of the interface between theEarth’s surface and its atmosphere, is a key variable in the determination of land surface–atmosphere processes from local to global scales
The objectives of the present paper are (1) to compare the LST measurements made over an asphalt surface using point measurements by an array of thermocouples, three narrow angle IR thermometers, one set of pyrgeometers with a nearly hemispheric field of view, and a forward looking infrared (FLIR) camera; (2) to assess how near-surface air temperature measurements made at the site compare with the ground-based LST
Our results show that the ground-based surface brightness temperature (BT) by the three infrared temperature sensors (IRT) over the entire period agreed quite well within

Summary

Introduction

Land surface temperature (LST), the thermodynamic temperature of the interface between theEarth’s surface and its atmosphere, is a key variable in the determination of land surface–atmosphere processes from local to global scales. The magnitude and temporal variation of LST is determined by the conductive, convective, and radiative energy exchange process at the earth atmosphere interface in response to the solar insolation and surface characteristics. LST, usually measured by ground-based, airborne, and space-borne remote sensing instruments, is the aggregated radiometric temperature of all surface components including soil, vegetation, and other land surface components within the sensor field of view in the direction of observation [8,9]. The measurement of LST by radiometric sensors, indicative of the thermal state of the surface, differs from near surface air temperature (AT) routinely measured at weather stations using a sheltered thermometer 1.5–3.5 m above a flat, grassy, well-ventilated surface or ground-surface temperature, usually measured by thermistors up to 5 cm beneath the surface cover [10]. As satellites do not directly measure AT, the satellite infrared-based LST measurements have been widely used for the indirect estimation of AT [11,12,13,14]

Objectives

Methods

Conclusion