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26 pages, 23434 KiB

Open AccessArticle

Accuracy Assessment of Photochemical Reflectance Index (PRI) and Chlorophyll Carotenoid Index (CCI) Derived from GCOM-C/SGLI with In Situ Data

by Taiga Sasagawa, Tomoko Kawaguchi Akitsu, Reiko Ide, Kentaro Takagi, Satoru Takanashi, Tatsuro Nakaji and Kenlo Nishida Nasahara

Remote Sens. 2022, 14(21), 5352; https://doi.org/10.3390/rs14215352 - 26 Oct 2022

Viewed by 3777

The photochemical reflectance index (PRI) and the chlorophyll carotenoid index (CCI) are carotenoid-sensitive vegetation indices, which can monitor vegetation’s photosynthetic activities. One unique satellite named “Global Change Observation Mission-Climate (GCOM-C)” is equipped with a sensor, “Second Generation Global Imager (SGLI)”, which has the [...] Read more.

The photochemical reflectance index (PRI) and the chlorophyll carotenoid index (CCI) are carotenoid-sensitive vegetation indices, which can monitor vegetation’s photosynthetic activities. One unique satellite named “Global Change Observation Mission-Climate (GCOM-C)” is equipped with a sensor, “Second Generation Global Imager (SGLI)”, which has the potential to frequently and simultaneously observe PRI and CCI over a wide swath. However, the observation accuracy of PRI and CCI derived from GCOM-C/SGLI remains unclear in forests. Thus, we demonstrated their accuracy assessment by comparing them with in situ data. We collected in situ spectral irradiance data at four forest sites in Japan for three years. We statistically compared satellite PRI with in situ PRI, and satellite CCI with in situ CCI. From the obtained results, the satellite PRI showed poor agreement (the best:

r = 0.294

(

p < 0.05

)) and the satellite CCI showed good agreement (the best:

r = 0.911

(

p < 0.001

)). The greater agreement of satellite CCI is possibly because satellite CCI contained fewer outliers and satellite CCI was more resistant to small noise, compared to satellite PRI. Our results suggest that the satellite CCI is more suitable for practical use than the satellite PRI with the latest version (version 3) of GCOM-C/SGLI’s products. Full article

(This article belongs to the Special Issue Feature Papers for Section Biogeosciences Remote Sensing)

► Show Figures

Figure 1

Figure 1
<p>Locations of the four study sites where in situ data were collected.</p> Full article ">Figure 2
<p>Overviews of the four study sites. The silvery artificial structure in each photo is the observation tower. The date next to the site name indicates when we took each photo.</p> Full article ">Figure 3
<p>Examples of the instruments: MS-700, masking device, and Automatic-capturing Digital Fisheye Camera (ADFC) at (<b>a</b>) FHK and (<b>b</b>) TKY. At TSE and FJY, the instruments were installed basically in the same manner as (<b>a</b>) FHK, but FJY was not equipped with the masking device for MS-700. At TKY, an external motor rotates MS-700 to observe the incident and reflected light (<b>b</b>).</p> Full article ">Figure 4
<p>Examples of fisheye images taken by ADFC. These images were taken in 2019 at TKY. The bottom numbers represent day of year (DOY).</p> Full article ">Figure 5
<p>The relative spectral response (RSR) in the visible and near-infrared (NIR) range of Global Change Observation Mission-Climate (GCOM-C)/Second Generation Global Imager (SGLI). The original data was obtained from [<a href="#B58-remotesensing-14-05352" class="html-bibr">58</a>]. The solid black lines represent the wavelength at 531<math display="inline"><semantics> <mi mathvariant="normal">n</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math>, 570 <math display="inline"><semantics> <mi mathvariant="normal">n</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math>, and 645 <math display="inline"><semantics> <mi mathvariant="normal">n</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math>, originally used to derive the photochemical reflectance index (PRI) and the chlorophyll carotenoid index (CCI). The blue, green, and orange dotted lines are reflectance measured by MS-700 at FHK on 9 April 2020 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math>), 18 July 2020 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>200</mn> </mrow> </semantics></math>), and 26 October 2020 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>300</mn> </mrow> </semantics></math>), respectively. Each reflectance was observed at 10:31:00 (Japan standard time (JST)) on each day.</p> Full article ">Figure 6
<p>The location of each study site and the nearest pixel of GCOM-C/SGLI. The background true color image was created from Sentinel-2 level 2 products. The cyan circle indicates the location of the observation tower. The red square indicates a range of the nearest pixel of GCOM-C/SGLI.</p> Full article ">Figure 7
<p>Time series of <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>original</mi> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>simulated</mi> </msub> </semantics></math>, and <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> from 2018 to 2020 at the four study sites. The blue square is <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>original</mi> </msub> </semantics></math>, the red plus is <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>simulated</mi> </msub> </semantics></math>, the black circle is <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> not screened with the quality assessment (QA) flag, and the black cross is <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>original</mi> </msub> </semantics></math> screened with the QA flag. The gray bands are snow seasons, the orange bands are autumn colors seasons, the green dotted lines are leafing timings, and the red dotted lines are leaf falling timings.</p> Full article ">Figure 8
<p>Scatter plots between <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>simulated</mi> </msub> </semantics></math>. <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> was screened with the QA flag (QA <math display="inline"><semantics> <mrow> <mo>=</mo> <mspace width="3.33333pt"/> <mn>2</mn> </mrow> </semantics></math>). The dotted line represents the 1:1 line. The black solid line is the linear regression line. The shape of each point represents the year: the circle is 2018, the triangle is 2019, and the square is 2020. The color of each point corresponds to the DOY.</p> Full article ">Figure 9
<p>Time series of <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>original</mi> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>simulated</mi> </msub> </semantics></math>, and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> from 2018 to 2020 at the four study sites. The blue square is <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>original</mi> </msub> </semantics></math>, the red plus is <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>simulated</mi> </msub> </semantics></math>, the black circle is <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> not screened with the QA flag, and the black cross is <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>original</mi> </msub> </semantics></math> screened with the QA flag. The gray bands are snow seasons, the orange bands are autumn colors seasons, the green dotted lines are leafing timings, and the red dotted lines are leaf falling timings.</p> Full article ">Figure 10
<p>Scatter plots between <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>simulated</mi> </msub> </semantics></math>. <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> was screened with the QA flag (QA <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>). The dotted line represents the <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>:</mo> <mn>1</mn> </mrow> </semantics></math> line. The black solid line is the linear regression line. The shape of each point represents the year: the circle is 2018, the triangle is 2019, and the square is 2020. The color of each point corresponds to the DOY.</p> Full article ">Figure 11
<p>Scatter plots of snow-free PRI (<b>a</b>–<b>d</b>) and snow-free CCI (<b>e</b>–<b>h</b>). Satellite data were screened with the QA flag (QA <math display="inline"><semantics> <mrow> <mo>=</mo> <mspace width="3.33333pt"/> <mn>2</mn> </mrow> </semantics></math>). Additionally, satellite data observed in snow seasons were manually removed. The dotted line represents the <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>:</mo> <mn>1</mn> </mrow> </semantics></math> line. The black solid line is the linear regression line. The shape of each point represents the year. The color of each point corresponds to the DOY.</p> Full article ">Figure 12
<p>The spatial distribution of <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> on 9 October 2019 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>282</mn> </mrow> </semantics></math>) around FHK. The cyan circles in each figure indicate the location of FHK. The red rectangle in (<b>a</b>) represents the range of (<b>b</b>–<b>d</b>). (<b>a</b>) shows the true color image of GCOM-C/SGLI. (<b>b</b>) shows the true color image, (<b>c</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math>, and (<b>d</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math>. (<b>a</b>,<b>b</b>) are not screened with the QA flag and (<b>c</b>,<b>d</b>) are screened with the QA flag. The black area represents where the RSRF product was unavailable, and the white area represents the screened area with the QA flag.</p> Full article ">Figure 13
<p>The sky images taken by upward ADFC around the observation time of GCOM-C/SGLI (10:46:44 (JST)) at FHK on 9 October 2019 (DOY = 282).</p> Full article ">Figure 14
<p>The spatial distribution of <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> on 2 August 2019 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>214</mn> </mrow> </semantics></math>) around TKY. The cyan circles in each figure indicate the location of TKY. The red rectangle in (<b>a</b>) represents the range of (<b>b</b>–<b>d</b>). (<b>a</b>) shows the true color image of GCOM-C/SGLI. (<b>b</b>) shows the true color image, (<b>c</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math>, and (<b>d</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math>. (<b>a</b>,<b>b</b>) are not screened with the QA flag and (<b>c</b>,<b>d</b>) are screened with the QA flag.</p> Full article ">Figure 15
<p>The spatial distribution of (<b>a</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>05</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>06</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math>, and (<b>c</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>08</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math> on 2 August 2019 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>214</mn> </mrow> </semantics></math>) around TKY. The range of each map is the same as that of <a href="#remotesensing-14-05352-f014" class="html-fig">Figure 14</a>b–d. All maps are screened with the QA flag. The cyan circles in each figure indicate the location of TKY.</p> Full article ">Figure 16
<p>The spatial distribution of <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> on 8 August 2018 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>220</mn> </mrow> </semantics></math>) around TSE. The cyan circles in each figure indicate the location of TSE. The red rectangle in (<b>a</b>) represents the range of (<b>b</b>–<b>d</b>). (<b>a</b>) shows the true color image of GCOM-C/SGLI. (<b>b</b>) shows the true color image, (<b>c</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math>, and (<b>d</b>) shows <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math>. (<b>a</b>,<b>b</b>) are not screened with the QA flag and (<b>c</b>,<b>d</b>) are screened with the QA flag.</p> Full article ">Figure 17
<p>The spatial distribution of (<b>a</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>05</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>06</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math>, and (<b>c</b>) <math display="inline"><semantics> <mrow> <mi mathvariant="italic">VN</mi> <msub> <mn>08</mn> <mi>satellite</mi> </msub> </mrow> </semantics></math> on 8 August 2018 (DOY <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>220</mn> </mrow> </semantics></math>) around TSE. The range of each map is the same as that of <a href="#remotesensing-14-05352-f016" class="html-fig">Figure 16</a>b–d. All maps are screened with the QA flag. The cyan circles in each figure indicate the location of TSE.</p> Full article ">Figure 18
<p>Scatter plots of spatial mean of <math display="inline"><semantics> <msub> <mi mathvariant="italic">PRI</mi> <mi>satellite</mi> </msub> </semantics></math> (<b>a</b>–<b>d</b>) and <math display="inline"><semantics> <msub> <mi mathvariant="italic">CCI</mi> <mi>satellite</mi> </msub> </semantics></math> (<b>e</b>–<b>h</b>) calculated from four neighbor pixels. Satellite data were screened with the QA flag (QA <math display="inline"><semantics> <mrow> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>). The error bar represents standard deviation for each point. The dotted line represents the <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>:</mo> <mn>1</mn> </mrow> </semantics></math> line. The black solid line is the linear regression line. The shape of each point represents the year. The color of each point corresponds to the DOY.</p> Full article ">Figure 19
<p>The downward fisheye images taken by ADFC in 2018 at (<b>a</b>) TSE, (<b>b</b>) TKY, (<b>c</b>) FJY, and (<b>d</b>) FHK. The numbers under the images are DOY when the images were taken. The images approximately display the approximately same observation area as downward MS-700 for each site.</p> Full article ">Figure A1
<p>The scatter plots of simulated band value and satellite band value used for calculation of PRI and CCI. The shape of each point represents the year. The color of each point corresponds to the DOY. Note that the range of the x-axis and y-axis is limited from 0 to 0.1, so a few points out of the range are not displayed.</p> Full article ">

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