You are plotting it incorrectly.
Use this:
loglog(f_pressure, Pxxc_pressure, 'r', 'LineWidth', 1.5);
instead of:
loglog([f_pressure(conf_level), f_pressure(conf_level)], [confdn, confup], 'r', 'LineWidth', 1.5);
and other incidents with similar code.
Note that ‘conf_level’ is a scalar with a single value (100), so it will only plot the confidence level at that one point. If that is the only value you want to plot, add that subscript to my code, and change the 'r' to a red marker of some type (perhaps '.r') so it will plot points instead of a line connecting them.
I changed all of them to produce this —
% data_uv = load('D5_SN111.dat'); % u, v data
data_uv = load('D5_SN111.txt'); % u, v data
% data_pressure = load('D5_SN111(1).dat'); % pressure data
data_pressure = load('D5_SN111(1).txt'); % pressure data
u = data_uv(:, 7); % u 성분 (7번째 열)
v = data_uv(:, 8); % v 성분 (8번째 열)
% D5_SN111(1).dat: year month day hour minute sec pressure
pressure = data_pressure(:, 7); % pressure data
pressure = fillmissing(pressure, 'linear');
u = fillmissing(u, 'linear');
v = fillmissing(v, 'linear');
WINDOW = 1024 * 2;
NOVERLAP = 512 * 2;
NFFT = 1024 * 2;
Fs = 1; % (1 sample/hour)
confcen = 10; %
conf_level = 100; %
%% pressure data PSD
figure;
[pxx_pressure, f_pressure, Pxxc_pressure] = pwelch(pressure, WINDOW, NOVERLAP, NFFT, Fs, 'ConfidenceLevel', 0.95);
figure
loglog(f_pressure, pxx_pressure, 'k'); % 파워 스펙트럼 밀도 그래프
hold on;
confup = Pxxc_pressure(conf_level, 2) ./ pxx_pressure(conf_level) * confcen
confdn = Pxxc_pressure(conf_level, 1) ./ pxx_pressure(conf_level) * confcen
loglog(f_pressure, Pxxc_pressure, 'r', 'LineWidth', 1.5);
title('Power spectra of bottom pressure at D5');
xlabel('Frequency (Hz)');
ylabel('Power/frequency (dbar^2/Hz)');
grid on;
legend('PSD', '95% Confidence Interval');
hold off;
%% u data's PSD
figure;
[pxx_u, f_u, Pxxc_u] = pwelch(u, WINDOW, NOVERLAP, NFFT, Fs, 'ConfidenceLevel', 0.95);
loglog(f_u, pxx_u, 'b');
hold on;
confup = Pxxc_u(conf_level, 2) ./ pxx_u(conf_level) * confcen;
confdn = Pxxc_u(conf_level, 1) ./ pxx_u(conf_level) * confcen;
loglog(f_u, Pxxc_u, 'r', 'LineWidth', 1.5)
% loglog([f_u(conf_level), f_u(conf_level)], [confdn, confup], 'r', 'LineWidth', 1.5);
title('Power spectra of U at D5');
xlabel('Frequency (Hz)');
ylabel('Power/frequency ((cm/s)^2/Hz)');
grid on;
legend('PSD', '95% Confidence Interval');
hold off;
%%v data's PSD
figure;
[pxx_v, f_v, Pxxc_v] = pwelch(v, WINDOW, NOVERLAP, NFFT, Fs, 'ConfidenceLevel', 0.95);
loglog(f_v, pxx_v, 'g');
hold on;
confup = Pxxc_v(conf_level, 2) ./ pxx_v(conf_level) * confcen;
confdn = Pxxc_v(conf_level, 1) ./ pxx_v(conf_level) * confcen;
% loglog([f_v(conf_level), f_v(conf_level)], [confdn, confup], 'r', 'LineWidth', 1.5);
loglog(f_v, Pxxc_v, 'r', 'LineWidth', 1.5);
title('Power spectra of V at D5');
xlabel('Frequency (Hz)');
ylabel('Power/frequency ((cm/s)^2/Hz)');
grid on;
legend('PSD', '95% Confidence Interval');
hold off;
.
