ETM+

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doi: lO.l016/SO273-1177(03)00687-2

DETECTION OF SURFACE TEMPERATURE FROM LANDSAT-7/ETM+ Y. Suga’, H. Ogawa’, K. Ohno’, and K. Yamada’ ‘Hiroshima Institute of Technology, 2-1-1, Miyake, Saeki-ku, Hiroshima 731-5193, JAPAN 2Hiroshima Earth Environment Information Centel; 2-1-1, Miyake, Saeki-ku, Hiroshima 731-5193, JAPAN ABSTRACT

Hiroshima Institute of Technology (HIT) in Japan has established a LANDSAT- Ground Station in cooperation with NASDA for receiving and processing the ETM+ data on March 15th, 2000 in Japan. The authors performed a verification study on the surface temperature derived from thermal infrared band image data of LANDSAT-7/Enhanced Thematic Mapper Plus (ETM+) for the estimation of temperatures around Hiroshima city and bay area in the western part of Japan as a test site. As to the thermal infrared band, the approximate functions for converting the spectral radiance into the surface temperature are estimated by considering both typical surface temperatures measured by the simultaneous field survey with the satellite observation and the spectral radiance observed by ETM+ band 6 ( 10.40- 125Opm), and then the estimation of the surface temperature distribution around the test site was examined. In this study, the authors estimated the surface temperature distribution equivalent to the land cover categories around the test site for establishing a guideline of surface temperature detection by LANDSAT-7/ETM+ data. As the result of comparison of the truth data and the estimated surface temperature, the correlation coefficients of the approximate function referred to the truth data are from 0.9821 to 0.9994, and the differences are observed from +0.7 to -1.5’C in summer, from +0.4 to -0.9OC in autumn, from -1.6 to -3.4OC in winter and from +0.5 to -0.5’C in spring season respectively. It is clearly found that the estimation of surface temperature based on the approximate functions for converting the spectral radiance into the surface temperature referred to the truth data is improved over the directly estimated surface temperature obtained from satellite data. Finally, the successive seasonal change of surface temperature distribution pattern of the test site is precisely detected with the temperature legend of 0 to 80°C derived from LANDSAT-7/ETM+ band 6 image data for the thermal environment monitoring. 0 2003 COSPAR.Published by Elsevier Ltd. All rights reserved.

INTRODUCTION

LANDSAT- was launched on April 15th, 1999 and images large areas of the sunlit earth daily by revisiting the same areas every 16 days. It has the ETM+ sensor, a multi-spectral scanning radiometer with eight bands and is capable of providing high-resolution image information of the Earth’s surface. The ETM+ acquires the image data in the visible (band 1: 0.45-0.52, band 2: 0.53-0.61, and band 3: 0.63-0.69 pm), near infrared (band 4: 0.78-0.90 pm), shortwave infrared (band 5: 1.55-1.75 and band 7: 2.09-2.35 pm), thermal infrared (band 6: 10.40-12.50 pm), and panchromatic (band 8: 0.52-0.90 pm). The spatial resolution is 15m in the panchromatic band, 30m in the visible, near infrared and shortwave infrared bands, and 60m in the thermal infrared band and each scene represents 183 by 170 kilometers on the earth. The Hiroshima Institute of Technology (HIT) in Japan established a LANDSAT- Ground Station for receiving and processing the ETM+ data on March 15”, 2000. At the beginning of this research, the authors examine the verification of the surface temperature derived from the shortwave infrared and thermal infrared bands image data of the ETM+. The items of the verification study are the estimation of the temperatures around the Hiroshima city and bay area using the ETM+ band 6 image. The surface temperature estimation is necessary to establish the monitoring systems of the heat islands in urban areas, sea surface temperature, thermal drainage distribution, forest fires and volcanic activities, etc. by using satellite remote sensing, and those systems provide us with the countermeasures for the environmental issues and the prediction methodologies for the natural disasters. So far, many researchers have reported their verification studies on the surface temperature from LANDSAT-S/TM Adv. Space Res. Vol. 32, No. 11, pp. 2235-2240.2003 Q 2003 COSPAR. Published by Elsevier Ltd. All rights Printed in Great Britain 0273-l 177/$30.00 + 0.00

reserved

2236

Y. Suga et al.

and NOAA/AVHRR data (Rothery et al. 1988, Rothery et al. 1990, Franca et al. 1994, Schneider et al. 1996, Urai 2000). TEST SITE AND DATA The test sites for the verification study of the surface temperature from the ETM+ image data are selected the surroundings of Hiroshima city and bay area in the western part of Japan and includes typical urban, agricultural and industrial areas along the coast. Figure 1 shows the LANDSAT-7/ETM+ color composite image (red: band 7, green: band 5 and blue: band 1) received and processed by HIT on 22 July 2000. The LANDSAT-7/ETM+ Level 1G data products used in this study are four successive seasons of data, path 112 and row 36, which were captured on 22 July 2000, 24 September 2000,29 December 2000 and 4 April 2001. SURFACE TEMPERATURE LANDSAT-7/ETM+

DETECTION

FROM

Fig. 1. LANDSAT-7/ETM+ color composite image (red: band 7, green: band 5 and blue: band 1) including the surroundings of Hiroshima city and bay area.

In this study, the authors conduct a verification study on the surface temperature using thermal infrared bands image data of the ETM+ for the estimation of the temperatures around Hiroshima city and bay area in the western part of Japan. For the surface temperature detection, the radiation emitted from the surface is measured using the ETM+ sensor, Truth Field Observations for Calibration and Validation The truth field observations were performed with respect to measurement of surface temperature simultaneous with the satellite observation using portable thermometers in each land cover category. The sea surface, rice plants in paddy fields, grass in golf links, asphalt pavement in port and the insulation material on a roof of a building were selected to cover the dynamic range of the surface temperature in the study area as shown in Figure 2. These truth data of surface temperature are used to calibrate ETM+ band 6 data for the estimation of absolute brightness temperature and the validation of estimated surface temperature. Portable thermometers were calibrated with reference to a standardized thermistor prior to perform the truth observation. As the result of the experiment of calibration for portable thermometers, the correlation coefficients were obtained from 0.9986 to 0.9996 compared with a standardized thermistor in the rage of 0 to 8O’C. Surface Temperature Detection from Thermal Band of ETM+ Planck’s radiation equation can be used to convert the measured spectral radiance to the temperature: L, = 2rrhc2h-5z,&c{exp(hc/WtT)-l}],

(1)

where h is the wavelength in pm, Ln is the spectral radiance in W.m~2ster-1+tm~‘, h is Planck’s constant, 6.626~1O”~Js, k is Boltzmann’s constant, 1.380~1O-~~JK-‘, T is temperature in K, c is the speed of light, 2.998x108mi’, 21 is the atmospheric transmittance and Q, is the spectral emissivity. Then the conversion equation from the spectral radiance into the temperature can be obtained as follows: T = c, /[&[(r,~,c,h-’

/XL,)+

l}],

(2)

where cl = 2rrhc and c2 = hc I k. LANDSAT-7/ETM+ data are acquired as 8 bits gray-scale imagery in the Level 1G products. The equation and constants for converting the 8 bit digital number (DN) of the image data into the spectral radiance is as follows:

Detection

of Sea Surface

LX = Lmin

+ &ax

Temperature - Lmin)

from Landsat-7iETM+ X DN

2237

(3)

/ DNrnax,

where LA is the spectral radiance in Wm2ster~‘~pm-’ received by the sensor for the pixel in question. Lmin is the minimum detected spectral radiance for the scene and L,, is the maximum detected spectral radiance for the scene. DN,, is the maximum value of the gray-level (=255), and DN is the gray-level for the pixel in question. The spectral radiance value is converted from DN in each pixel by using Eq. (3) and then it can be substituted in Eq. (2) to compute the temperature. The satellite level spectral radiance at various temperatures from Eq. (1) is shown in Figure 3. We can recognize that the intensity of emitted radiation increases with the peak shifting towards shorter wavelength as the temperature rises. oFigure 3 shows that the band 6 in the thermal infrared range can measure the temperature in the range of -70 - +90 C in the low gain mode and -30 - +60 C in the high gain mode, respectively. Parameters such as the wavelength range, L,, and L,,,, etc. are in Landsat 7 Science Data User Handbook (USGS, 2000). At the Hiroshima city and bay area test site, the authors conducted a field survey simultaneous with the satellite observation and measured typical surface temperatures. By considering the truth data measured by the field survey and the spectral radiance converted from the DN data of the ETM+ band 6, approximate functions for converting the spectral radiance into the surface temperature are estimated by the least square method. Then the surface temperature distribution around Hiroshima city and bay area is estimated. In this study, the atmospheric transmittance, rais assumed to be 0.93 in each season at midlatitude, and spectral emissivity, EXis alsa assumed to be 0.98 respectively according to the references so far.

Sea surface in bay

LANDSAT-7/ETM+ band 6 image

Asphalt pavement in port

Fig. 2. Truth field observation at each land cover category and IANDSAT-7/ETM+ band 6 image in the study area.

GENERATION

OF SURFACE TEMPERATURE

IMAGE FROM LANDSAT-7/ETM+

The estimated surface temperature directly obtained from satellite data (broken line) based on the above mentioned processing is partly overestimated and underestimated as shown in Figure 4. This will have to be refined. Therefore, the authors conducted field surveys in each land cover category using portable thermometers in Hiroshima city simultaneous with the satellite observations in four successive seasons of LANDSAT-7/ETM+

Y. Suga et al.

2238

Wave Length (p m) Fig. 3. Satellite level radiance at various surface temperatures. Uniform atmospheric transmittance of 1.0 and surface emissivity of 1.0 are assumed. Vertical columns indicate the bands and dynamic ranges of LANDSAT-7/ETM+ sensor (modified Rothery et. al 1988 for LANDSAT-7/ETM+).

data bath 112 and row 36). In order to span a wide range of surface temperature, the sea surface, paddy fields, grass in golf links, asphalt pavement and the insulation material on a roof of the building were selected for the field and the satellite observations. The approximate functions for converting the spectral radiance into the surface temperature for low gain and high gain modes on 22 July 2002 are estimated as follows: L lowgain

=4.5623e-4xT2 - 0.2559xT+44.8410, xT2 - 0.2794XT + 48.3504,

Lfighgain=4.9406e-4

where

bowgain

ad

Lhighgain

(4)

(5)

are the spectral radiance in low gain and high gain modes, respectively, and T is the

Table 1. The truth data measured by the field survey, the spectral radiance in low and high gain modes and the estimated surface temperature Spectral radiance in low gain and high gain modes [W.rn-*.stei’qm”] Low gain mode High gain mode

Observationdate.

Land cover category

Truth surface temperature [“Cl

22 July 2000

Sea Surface Rice plant Grass Asphalt Insulation Material

26.5 31.5 36.0 46.9 68.0

9.0880 9.2216 9.3553 9.6226 10.6249

8.9965 9.0337 9.2197 9.5174 10.5219

26.7 31.1 35.4 45.4 68.7

25.3 28.0 32.0 38.9 62.1

8.8875

8.7361

9.0212 9.0880

8.9593

24 September 2000

Sea Surface Rice plant Grass Asphalt Insulation Material

24.5 27.8 31.1 38.9 62.5

Sea Surface Rice plant Grass Asphalt Insulation Material

13.9

Sea Surface Rice plant Grass Asphalt Insulation Material

12.1 18.3 28.1 25.5 41.4

29 December 2000

4 April 2001

8.2 12.1 9.0 16.8

9.4889

8.7733 9.4057

10.6249

10.6707

7.4174 7.0833 7.3506 7.1501

7.2851 6.9502 7.2107

7.8184 7.7515 8.2861 9.0880 8.9544 10.2908

7.0619 7.6943 7.6199 8.2152 8.9593 8.8477

10.2243

Estimated surface temperature [“Cl

10.5 6.0 9.6 6.9 15.2 12.1 18.3 27.6 26.0 41.4

Detection

of Sea Surface

Temperature

from Landsat-7/ETM+

2239

surface temperature in Kelvins. The surface temperatures for the five land cover categories estimated by using the functions above are also indicated in Table 1. The result supports the fact that the surface temperature is estimated appropriately. Table 1 shows the truth data and the spectral radiance from the DN data of the ETM+ band 6. The correlation coefficients between typical surface temperatures and the spectral radiance in Table 1 are from 0.982 1 to 0.9994 for the low gain mode and from 0.9653 to 0.9987 for the high gain mode in each season. As for another season data, the above same processing is adopted and the appropriate results are also obtained as shown in Table 1. Figure 4 shows also the correlation between the truth surface temperature and the estimated st@ace temperature (solid line), and the differences are observed from +0.7 to -1.5 C in summer, from +0.4 to -0.9 C in autumn, from -1.6 to -3.4’C in winter and from +0.5 to 0.5OC in spring season respectively. The largest difference is observed in winter because the distribution of actual surface temperature on the ground is low and narrow. It is clearly found that the estimation of surface temperature based on the approximate functions for converting the spectral radiance into the surface temperature referred to the truth data is improved relative to the directly estimated surface temperature obtained from satellite data. Figure 5 shows the color-coded surface temperature images in the surroundings of Hiroshima city and bay area derived from the ETM+ band 6 image data. The white colored part depicts cloud in each image. The surface temperature distribution in Figure 5 is equivalent to the land cover categories and the sea. The surface temperature distribution of each image is also appropriate in comparison with field survey truth data in each season. It is clearly found that the successive seasonal cOhangeof surface temperature distribution pattern of the test site is precisely detected with the legend from 0 to 80 C. The heat island phenomena are clearly0detected in urbanized area from summer to spring season respectively. The high temperatures around 70 to 80 C are observed at the circled area of the city in each season. There are large automobile factories and also steel mills. From these results, it is proved that the authors can qualitatively and quantitatively verify the surface temperature derived from LANDSAT-7/ETM+ band 6 image data for the thermal environment monitoring in land and sea.

5E .9 273v 273

I 293

, 313

Truth

surface

temperature

1 333

I 353

(K)

i

/ kO.9977 273

273

Truth

22 July 2000

293

Truth

Fig. 4.

Correlation

surface temperature 29 December 2000

between

estimated

(K)

surface

Truth

temperature

/

I 313

I 333

surface temperature 24 September 2000

(K)

313

333

surface temperature 4 April 2001

(K)

I 353

and truth observation.

CONCLUSION

In this study, the authors conducted a verification study on the surface temperature derived from LANDSAT-

,@“I 0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

-I”cl

Fig. 5. Surface temperature detection images around Hiroshima city and-bay area derived from four successive seasons of LANDSAT-7IETM+ data.

7/ETM+ data using the thermal intked band for the estimation of temperatures around the Hiroshima city and bay area in the western part of Japan. The authors conducted field surveys in each land cover category using portable thermometers in the test site simultaneous with the satellite observation during four successive seasons of LANDSAT-7/ETM+ data. The approximate functions for converting the spectral radiance into the surface temperature are estimated for improving so that the estimated surface temperature directly obtained from satellite data is partly overestimated and underestimated. As the result of comparison of the truth data and the estimated surface temperature, the correlation coefficients of the approximate function referred to the truth data are from 0.9821 to 0.9994, and the difference of estimation and truth observation is obtained from 0 to 1.5 C except for winter season. It is clearly found that the estimation of surface temperature based on the approximate functions for converting the spectml radiau~ into the surface tempersture referred to the truth data is improved than the directly estimated surface temperature obtained from satellite data. Finally, the successive seasonal c+ge of surface temperature distribution pattern of the test site is precisely detected with the legend from 0 to 80 C, it is proved that the authors can qualitatively and quantitatively verity the surface temperature derived from LANDSAT-7/ETM+ band 6 image data for the thermal environment monitoring in land and sea. For further study, the authors plan the modification of the approximate functions for converting the spectral radiance into the surface temperature by the field and satellite observation throughout a year, and the development of thermal anomaly monitoring systems for disaster and environmental issues. In this study, the atmospheric transmittance and spectral emissivity are assumed. Therefore, the effect of atmospheric transmittance and spectral emissivity should be precisely considered in further study. REFERENCES

ERDAS, Inc., ERDAS Field Guide, 1999. Franca GB., and A.P. Cracknell, Retrieval of land and sea surface temperature using NOAA-11 AVHRR data in north-eastem Brazil. International Journal of Remote Sensing, 15,1695-1712,1994. GEOSYSTEMS GmbH, ATCOR for ERDAS ZMGLVE, 2002. Rothery D.A., P.W. Francis, and CA. Wood, Volcano monitoring using short wavelength infrared data from satellites. Journal of Geophysical Research, 93,7993-8008,1988. Rothery D.A., and P.W. Francis, Short wavelength infrared images for volcano monitoring, International Journal of Remote Sensing, 10, 1665-1667, 1990. Schneider K., and W. Mauser, Processing and accuracy of Landsat Thematic Mapper data for lake surface temperature measutements. International Journal of Remote Sensing, 17,2027-2041. 1996. Spectral Sciences, Inc., MODTR4N4 USER ‘S MANUAL, 2000. Urai M, Volcano monitoring with Landsat TM short-wave infrared bands: the 1990-1994 eruption of Unzen Volcano, Japan. Intemational Joumal of Remote Sensing, 21,861-872,200O. USGS, Landsat 7 Science Data Users Handbook, 2000. E-mail address of Y. Suga [email protected] Manuscript received 10 Gctober 2002; revised 2 December, accepted 18 February 2003