l0 = const.c / cfg.radar.f0
# along tr. bw [rad]
a_bw = l0 / cfg.radar.microsat_antenna
off_nadir = np.radians(cfg.radar.off_nadir)
# calculate orbit
alt0 = cfg.orbit.alt
inc = cfg.orbit.inc
e = cfg.orbit.e
re_cycle_num = cfg.orbit.re_cycle_num
re_day = cfg.orbit.re_day
if np.size(alt0) > 1:
alt = np.zeros_like(alt0)
v = np.zeros_like(alt0)
dis = np.zeros_like(alt0)
for i in range(np.size(alt0)):
alt[i], v[i], dis[i] = orbit_com(alt0[i], inc, e, re_cycle_num, re_day,
cfg.orbit.con_repeat)
else:
alt, v, dis = orbit_com(alt0, inc, e, re_cycle_num, re_day)
alt = alt / np.cos(a_bw / 2 + off_nadir)
B_amb = l0 * alt / 2 * np.sin(np.radians(cfg.scene.slope)) / baseline.reshape(
(baseline.shape + (1, )))
if np.size(cfg.scene.slope) > 1:
# antenna & peak power
# plot figures
leg = []
plt.figure()
for i in range(np.size(cfg.scene.slope)):
plt.plot(baseline, B_amb[:, i])
leg = np.append(leg, ["Scene slope=%d deg" % (cfg.scene.slope[i])])
def performance_tool(cfg_file, concept, SAR_mode_enable,
interleaved_mode_enable):
# INITIAL PARAMETERS
cfg = tpio.ConfigFile(cfg_file)
# lambda [m]
l0 = const.c / cfg.radar.f0
# along tr. bw [rad]
a_bw = l0 / cfg.radar.az_ant
# cross tr. bw [rad]
c_bw = l0 / cfg.radar.c_ant
# along tr. eff. or smallest bw [deg]
eff_a_bw = a_bw / np.sqrt(2)
# cross tr. eff. or smallest bw [deg]
eff_c_bw = c_bw / np.sqrt(2)
# antenna gain
gain_t = 10 * np.log10(4 * np.pi / a_bw / c_bw / 2)
gain_r = gain_t
# compressed pulse length
pw = const.c / 2 / cfg.radar.bandwidth
# calculate orbit
alt0 = cfg.orbit.alt
inc = cfg.orbit.inc
e = cfg.orbit.e
re_cycle_num = cfg.orbit.re_cycle_num
re_day = cfg.orbit.re_day
if np.size(alt0) > 1:
alt = np.zeros_like(alt0)
v = np.zeros_like(alt0)
dis = np.zeros_like(alt0)
for i in range(np.size(alt0)):
alt[i], v[i], dis[i] = orbit_com(alt0[i], inc, e, re_cycle_num,
re_day, cfg.orbit.con_repeat)
else:
alt, v, dis = orbit_com(alt0, inc, e, re_cycle_num, re_day)
# mode recognize
if concept == "Specular Constellation":
# along tr. bw [rad]
a_bw = l0 / cfg.radar.microsat_antenna_along
# cross tr. bw [rad]
c_bw = l0 / cfg.radar.microsat_antenna
eff_a_bw = a_bw / np.sqrt(2)
alt_m = alt / np.cos(a_bw / 2)
gain_t = 10 * np.log10(4 * np.pi / a_bw / c_bw / 2) - 3
if cfg.sim.max_coverage:
gain_r = 10 * np.log10(4 * np.pi / c_bw / c_bw / 2)
if cfg.sim.interferometer_enable:
# based on Ulaby model if consider the ocean surface is mirror alph=1
# at far range the SNR should be enough
D = (np.tan(np.radians(cfg.radar.off_nadir)) * alt +
c_bw / 2 * alt) * 2
off_nadir = np.arctan(
(D / 2 + np.radians(cfg.radar.off_nadir) / 2 * alt) /
alt) # maximal off-nadir angle
gain_r = gain_r - 10 * np.log10(4.34 * np.degrees(off_nadir)) - 3
else:
gain_r = gain_r - 3
if SAR_mode_enable:
pulse_coh_bur = cfg.radar.pulse_coh_bur
else:
pulse_coh_bur = 1
if cfg.sim.plot_spec_coverage:
if np.size(cfg.radar.microsat_antenna) > 1:
ang = l0 / cfg.radar.microsat_antenna
plt.figure()
for i in range(np.size(alt_m)):
plt.plot(cfg.radar.microsat_antenna,
ang * cfg.orbit.alt[i] / 1000)
leg = np.append(
leg, ["Orbit height=%d km" % (cfg.orbit.alt[i] / 1000)])
plt.xticks(fontsize=16)
plt.yticks(fontsize=16)
plt.xlabel('Cross-track size of microcube (m)', fontsize=16)
plt.ylabel('Coverage area (km)', fontsize=16)
plt.title(concept)
plt.legend(leg)
# plt.ylim(2, 5)
plt.grid()
# calculation performance
# Doppler BW [Hz] and prf
Dop_bw = 2 * v / (l0 / eff_a_bw)
if SAR_mode_enable:
prf = 18700
else:
prf = 4000 #int(1.4 * Dop_bw)
prf_r = 1.4 * Dop_bw
if cfg.sim.plot_prf:
#plot the prf rule
fig = plt.figure()
ax1 = fig.add_subplot(111)
ax1.plot(l0 / a_bw, prf_r)
#ax1.set_xticks(fontsize=16)
#ax1.set_yticks(fontsize=16)
ax1.set_xlabel('Along-track antenna dimension of the Microsat (m)',
fontsize=16)
ax1.set_ylabel('PRF (Hz)', fontsize=16, color="blue")
ax1.set_title("PRF vs. swath")
ax2 = ax1.twinx()
ax2.plot(l0 / a_bw,
l0 / (1 / cfg.radar.microsat_antenna_along) * alt_m / 1000,
'r')
ax2.set_ylabel('Cross-track swath length (km)',
fontsize=16,
color="red")
plt.show()
plt.grid()
prt = 1 / prf
# free space between pulses [m]
#F_length = (prt - cfg.radar.pw_uc / 1000) / 2 * const.c
# max # pulses in burst [ ]
#max_pulse_burst = (alt * 2 / const.c / prt).astype(int)
# along tr. footprint [km]
al_res = eff_a_bw * alt
# cross tr. footprint [km]
# pulse interval time
if SAR_mode_enable:
bur_rep_int = cfg.radar.bur_rep_int
else:
bur_rep_int = prt * 1000
c_res = eff_c_bw * alt
# distance between bursts [m]
dis_burst = bur_rep_int * v / 1000
if cfg.sim.pulse_limited_enable:
# pulse limited radius on ground [m]
pul_rad = np.sqrt(2 * alt * pw)
# Pulse lim. resolution [m]
plu_res = 2 * pul_rad
if SAR_mode_enable:
# Synthetic Aperture length [m]
syn_length = 1 / prf * pulse_coh_bur * v
# SAR resolution [m]
sar_res = prf * alt * l0 / (2 * pulse_coh_bur * v)
# Raney limit [m]
raney_l = 3 * pw * alt / sar_res
# cells in Raney region
cel = cell_calculate(al_res, raney_l, sar_res)
# burst length [s]
bur_length = pulse_coh_bur * prt
# incoh. observ. per second
N_incoh = cel / bur_rep_int * 1000
# incoh. observ. per res. cell
N_incoh_r = cel * sar_res / v / bur_rep_int * 1000
else:
# cells in Raney region
cel = 1
sar_res = plu_res
# burst length [s]
bur_length = cfg.radar.pw_uc
if np.size(dis_burst) > 1 and np.size(sar_res) > 1:
N_incoh = np.zeros_like(dis_burst)
for i in range(np.size(N_incoh)):
if dis_burst[i] > 0.305 * alt[i] * l0 / sar_res[i]:
N_incoh[i] = cel / bur_rep_int * 1000
else:
N_incoh[i] = v / (0.305 * alt[i] * l0 / sar_res[i])
elif np.size(dis_burst) > 1 and np.size(sar_res) == 1:
N_incoh = np.zeros_like(dis_burst)
for i in range(np.size(N_incoh)):
if dis_burst[i] > 0.305 * alt * l0 / sar_res:
N_incoh[i] = cel / bur_rep_int[i] * 1000
else:
N_incoh[i] = v / (0.305 * alt * l0 / sar_res)
elif np.size(sar_res) > 1:
N_incoh = np.zeros_like(sar_res)
for i in range(np.size(sar_res)):
if dis_burst > 0.305 * alt * l0 / sar_res[i]:
N_incoh[i] = cel / bur_rep_int * 1000
else:
N_incoh[i] = v / (0.305 * alt[i] * l0 / sar_res)
else:
if dis_burst > 0.305 * alt * l0 / sar_res:
N_incoh = cel / bur_rep_int * 1000
else:
N_incoh = v / (0.305 * alt * l0 / sar_res)
N_incoh_r = N_incoh * sar_res / v
# power performance
KTF = -204 + cfg.loss.NF
# illuminated area [m2]
A = area_cal(sar_res, plu_res, pul_rad)
A0 = area_cal(plu_res, plu_res, pul_rad)
# Power calculation & accuracy
sigma = 10 * np.log10(A) + cfg.loss.sigma0
sigma_w = 10 * np.log10(A0) + cfg.loss.sigma0
# req. peak power [W]
if (np.size(cfg.loss.SNR) > 1):
P_r = ((4 * np.pi)**3 * alt**4 * 10**((cfg.loss.SNR.reshape(
(cfg.loss.SNR.shape +
(1, ))) + cfg.loss.loss_in_at + KTF - gain_t - gain_r - sigma) /
10) / l0**2 /
(cfg.radar.pw_uc / 1000) / pulse_coh_bur)
# req. av. power [W]
P_a = P_r * pulse_coh_bur * cfg.radar.pw_uc / bur_rep_int
else:
P_r = ((4 * np.pi)**3 * alt**4 *
10**((cfg.loss.SNR + cfg.loss.loss_in_at + KTF - gain_t -
gain_r - sigma) / 10) / l0**2 / (cfg.radar.pw_uc / 1000) /
pulse_coh_bur)
# req. av. power [W]
P_a = P_r * pulse_coh_bur * cfg.radar.pw_uc / bur_rep_int
# calculating the SNR before the compression processing
P_rc = cfg.radar.input_power * 10**(
(gain_t + gain_r - cfg.loss.loss_in_at + sigma_w) /
10) * l0**2 / (4 * np.pi)**3 / alt**4
noise = 10**(KTF / 10) * cfg.radar.bandwidth
SNR0 = 10 * np.log10(P_rc / noise)
P_rcw = 10 * np.log10(P_rc) + 30
noise_w = 10 * np.log10(noise) + 30
# single cell height accuracy [cm]
if (np.size(cfg.loss.SNR) > 1):
ac = pw / np.sqrt(2 * N_incoh_r *
(1 / (1 + 1 / 10**(cfg.loss.SNR.reshape(
(cfg.loss.SNR.shape + (1, ))) / 10)))) * 100
else:
ac = pw / np.sqrt(2 * N_incoh_r *
(1 / (1 + 1 / 10**(cfg.loss.SNR / 10)))) * 100
# raw data rate [Mb/s], 16 bit samples
raw_data_rate = pulse_coh_bur * cfg.radar.rg_num * 1000 / bur_rep_int / 1e6 * 16
# proc.per channel [kb/s]
if SAR_mode_enable:
proc_rate = v / sar_res * cfg.radar.rg_num * 16 / 1000
else:
proc_rate = 4 * cfg.radar.rg_num * 16 / 1000
if cfg.sim.interferometer_enable:
# cross track resolution [m]
if np.size(cfg.loss.SNR) > 1:
cross_res = 1 / np.sqrt(
10**(np.cos(a_bw / 2)**3 * cfg.loss.SNR.reshape(
(cfg.loss.SNR.shape + (1, ))) /
10)) * l0 * alt / (2 * np.pi * cfg.radar.baseline)
# This calculation is meaningless
# height_ac = cross_res / np.cos(a_bw / 2)
if interleaved_mode_enable:
P_a = P_r * prf * cfg.radar.pw_uc / 1000
if SAR_mode_enable:
N_incoh = cel / (pulse_coh_bur / prf)
else:
# cells in Raney region
if 1 / prf * v > 0.305 * alt * l0 / sar_res:
N_incoh = cel / pulse_coh_bur / prf
else:
N_incoh = min(v / (0.305 * alt * l0 / sar_res), prf)
# incoh. observ. per res. cell
N_incoh_r = cel * sar_res / v / pulse_coh_bur * prf
ac = pw / np.sqrt(2 * N_incoh_r *
(1 / (1 + 1 / 10**(cfg.loss.SNR.reshape(
(cfg.loss.SNR.shape + (1, ))) / 10)))) * 100
raw_data_rate = prf * cfg.radar.rg_num / 1e6 * 16
# analysis of cells in the raney region
if cfg.sim.plot_raney:
plt.figure()
plt.plot(l0 / a_bw, 2 * raney_l / 1000)
plt.xlabel('Along-track antenna dimension of the Microsat (m)',
fontsize=16)
plt.ylabel('Along-track footprint (km)', fontsize=16)
plt.plot(l0 / a_bw, al_res / 1000, 'r')
ax2.set_ylabel('Length (km)', fontsize=16)
plt.legend(['Raney region length', 'Along-track footprint'])
plt.show()
plt.grid()
fig = plt.figure()
ax1 = fig.add_subplot(111)
ax1.plot(l0 / a_bw, cel)
#ax1.set_xticks(fontsize=16)
#ax1.set_yticks(fontsize=16)
ax1.set_xlabel('Along-track antenna dimension of the Microsat (m)',
fontsize=16)
ax1.set_ylabel('cell number in the raney region',
fontsize=16,
color="blue")
ax2 = ax1.twinx()
ax2.plot(l0 / a_bw, ac, 'r')
ax2.set_ylabel('SSH accuracy', fontsize=16, color="red")
plt.show()
plt.grid()
return P_r, P_a, ac, raw_data_rate, proc_rate